Signalling of The Presence of Inter-Layer Reference Pictures

ABSTRACT

A method of video processing includes performing a conversion between a video including one or more pictures and a bitstream of the video, wherein the bitstream conforms to a format rule, wherein the format rule conditionally allows coding of a picture in one layer using reference pictures from other layers based on a first syntax element indicating whether the reference pictures from the other layers are present in the bitstream, and wherein the first syntax element is conditionally signaled in the bitstream based on a second syntax element that indicates whether an identifier of a parameter set associated with the picture is not equal to zero.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Patent ApplicationNo. PCT/US2021/012835, filed on Jan. 8, 2021, which claims the priorityto and benefits of U.S. Provisional Patent Application No. US 62/959,108filed on Jan. 9, 2020. All the aforementioned patent applications arehereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document relates to image and video coding and decoding.

BACKGROUND

Digital video accounts for the largest bandwidth use on the internet andother digital communication networks. As the number of connected userdevices capable of receiving and displaying video increases, it isexpected that the bandwidth demand for digital video usage will continueto grow.

SUMMARY

The present document discloses techniques that can be used by videoencoders and decoders for video encoding or decoding, and includesconstraints, restrictions and signalling for subpictures, slices, andtiles.

In one example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video and a bitstreamof the video, wherein the bitstream comprises one or more access unitsaccording to a format rule, and wherein the format rule specifies anorder in which a first message and a second message that apply to anoperation point (OP) are present within an access unit (AU) such thatthe first message precedes the second message in a decoding order.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video and a bitstreamof the video, wherein the bitstream comprises one or more access unitsaccording to a format rule, and wherein the format rule specifies anorder in which a plurality of messages that apply to an operation point(OP) are present within an access unit such that a first message of theplurality of messages precedes a second message of the plurality ofmessages in a decoding order.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprising apicture and a bitstream of the video, wherein the bitstream conforms toa format rule, wherein the format rule specifies that an indication ofwhether a first flag is signalled at a beginning of a picture headerassociated with the picture, wherein the first flag is indicative ofwhether the picture is an intra random access point (IRAP) picture or agradual decoding refresh (GDR) picture.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures and a bitstream of the video, wherein the bitstreamconforms to a format rule, wherein the format rule disallows coding of apicture of the one or more pictures to include a coded slice networkabstraction layer (NAL) unit having a gradual decoding refresh type andto associate with a flag indicating that the picture contains mixedtypes of NAL units.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures and a bitstream of the video, wherein the bitstreamconforms to a format rule, wherein the format rule allows coding of apicture of the one or more pictures to include a coded slice networkaccess layer (NAL) unit having a gradual decoding refresh type and toassociate with a flag indicating that the picture does not contain mixedtypes of NAL units.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a picture of a videoand a bitstream of the video, wherein the bitstream conforms to a formatrule that specifies whether a first syntax element is signalled in apicture parameter set (PPS) associated with the picture, wherein thepicture comprises one or more slices with a slice type, wherein thefirst syntax element indicates that the slice type is signalled in thepicture header due to the first syntax element being equal to zero, andotherwise indicates that the slice type is signalled in a slice header.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a picture of a videoand a bitstream of the video according to a rule, wherein the conversioncomprises an in-loop filtering process, and wherein the rule specifiesthat a total number of vertical virtual boundaries and a total number ofhorizontal virtual boundaries related to the in-loop filtering processare signalled at a picture-level or a sequence-level.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures and a bitstream of the video, wherein the bitstreamconforms to a format rule, wherein the format rule conditionally allowscoding of a picture in one layer using reference pictures from otherlayers based on a first syntax element indicating whether the referencepictures from the other layers are present in the bitstream, and whereinthe first syntax element is conditionally signalled in the bitstreambased on a second syntax element that indicates whether an identifier ofa parameter set associated with the picture is not equal to zero.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a picture of a videoand a bitstream of the video, wherein the bitstream conforms to a formatrule, wherein the format rule defines a first syntax element forenabling (a) a synchronization process for context variables beforedecoding a coding tree unit (CTU) in the picture and (b) a storageprocess for the context variables after decoding the CTU, wherein thefirst syntax element is signalled in a sequence parameter set (SPS)associated with the picture.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a picture of a videoand a bitstream of the video, wherein the bitstream conforms to a formatrule, wherein the format rule defines a syntax element for indicatingwhether signalling for entry point offsets for tiles or tile-specificCTU rows are present in a slice header of the picture, and wherein thesyntax element is signalled in a sequence parameter set (SPS) associatedwith the picture.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video and abitstream of the video according to a rule, wherein the rule specifiesthat a first syntax element, which indicates a number of parameters foran output layer set (OLS) hypothetical reference decoder (HRD) in avideo parameter set (VPS) associated with the video, is less than afirst predetermined threshold.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video and abitstream of the video according to a rule, wherein the rule specifiesthat a syntax element, which indicates a number of profile/tier/level(PTL) syntax structures in a video parameter set (VPS) associated withthe video, is less than a predetermined threshold.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video and abitstream of the video according to a rule, wherein the rule specifiesthat a first syntax element, which indicates a number of decoded picturebuffer parameters syntax structures in a video parameters set (VPS), maybe less than or equal to a second syntax element, which indicates anumber of layers specified by the VPS.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video and abitstream of the video according to a rule, wherein the rule allows aterminating network abstraction layer (NAL) unit to be made available toa decoder by signalling in the bitstream or providing through externalmeans.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video and abitstream of the video, wherein the bitstream conforms to a format rule,and wherein the format rule restricts each layer in the bitstream tocontain only one subpicture due to a syntax element being equal to zero,which indicates that the each layer is configured to use inter-layerprediction.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video and abitstream of the video according to a rule, wherein the rule specifiesthat a sub-bitstream extraction process is implemented to generate asub-bitstream for decoding, wherein the sub-bitstream extraction processis configured to extract, from the bitstream, a sub-bitstream with atarget highest temporal identifier, and wherein, the rule specifiesthat, during the extracting, upon removing a video coding layer (VCL)network abstraction layer (NAL) unit, filler data units and fillersupplemental enhancement information (SEI) messages in SEI NAL unitsthat are associated with the VCL NAL unit are also removed.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video unit of avideo and a bitstream of the video, wherein the bitstream conforms to aformat rule, wherein the format rule specifies that the bitstreamincludes a first syntax element, which indicates whether the video unitis coded in a lossless mode or in a lossy mode, and wherein signalling asecond syntax element, which indicates an escape sample in a palettemode applied to the video unit, is selectively included based on a valueof the first syntax element.

In yet another example aspect, a video encoder apparatus is disclosed.The video encoder comprises a processor configured to implement theabove-described methods.

In yet another example aspect, a video decoder apparatus is disclosed.The video decoder comprises a processor configured to implement theabove-described methods.

In yet another example aspect, a computer readable medium having codestored thereon is disclosed. The code embodies one of the methodsdescribed herein in the form of processor-executable code.

These, and other, features are described throughout the presentdocument.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of partitioning a picture with luma coding treeunits (CTUs).

FIG. 2 shows another example of partitioning a picture with luma CTUs.

FIG. 3 shows an example partitioning of a picture.

FIG. 4 shows another example partitioning of a picture.

FIG. 5 is a block diagram of an example video processing systemaccording to various embodiments of the disclosure.

FIG. 6 is a block diagram of an example hardware platform used for videoprocessing.

FIG. 7 is a block diagram that illustrates a video coding systemaccording to various embodiments of the disclosure.

FIG. 8 is a block diagram that illustrates an encoder according tovarious embodiments of the disclosure.

FIG. 9 is a block diagram that illustrates a decoder according tovarious embodiments of the disclosure.

FIGS. 10-26 show flowcharts for example methods of video processing.

DETAILED DESCRIPTION

Section headings are used in the present document for ease ofunderstanding and do not limit the applicability of techniques andembodiments disclosed in each section only to that section. Furthermore,H.266 terminology is used in some description only for ease ofunderstanding and not for limiting scope of the disclosed techniques. Assuch, the techniques described herein are applicable to other videocodec protocols and designs also.

1. Introduction

This document is related to video coding technologies. Specifically, itis about signalling of subpictures, tiles, and slices. The ideas may beapplied individually or in various combinations, to any video codingstandard or non-standard video codec that supports multi-layer videocoding, e.g., the being-developed Versatile Video Coding (VVC).

2. Abbreviations

-   -   APS Adaptation Parameter Set    -   AU Access Unit    -   AUD Access Unit Delimiter    -   AVC Advanced Video Coding    -   CLVS Coded Layer Video Sequence    -   CPB Coded Picture Buffer    -   CRA Clean Random Access    -   CTU Coding Tree Unit    -   CVS Coded Video Sequence    -   DPB Decoded Picture Buffer    -   DPS Decoding Parameter Set    -   EOB End Of Bitstream    -   EOS End Of Sequence    -   GDR Gradual Decoding Refresh    -   HEVC High Efficiency Video Coding    -   HRD Hypothetical Reference Decoder    -   IDR Instantaneous Decoding Refresh    -   JEM Joint Exploration Model    -   MCTS Motion-Constrained Tile Sets    -   NAL Network Abstraction Layer    -   OLS Output Layer Set    -   PH Picture Header    -   PPS Picture Parameter Set    -   PTL Profile, Tier and Level    -   PU Picture Unit    -   RBSP Raw Byte Sequence Payload    -   SEI Supplemental Enhancement Information    -   SPS Sequence Parameter Set    -   SVC Scalable Video Coding    -   VCL Video Coding Layer    -   VPS Video Parameter Set    -   VTM VVC Test Model    -   VUI Video Usability Information    -   VVC Versatile Video Coding

3. Initial Discussion

Video coding standards have evolved primarily through the development ofthe well-known International Telecommunication Union (ITU)Telecommunication Standardization Sector (ITU-T) and InternationalOrganization for Standardization (ISO)/International ElectrotechnicalCommission (IEC) standards. The ITU-T produced H.261 and H.263, ISO/IECproduced MPEG-1 and MPEG-4 Visual, and the two organizations jointlyproduced the H.262/MPEG-2 Video and H.264/MPEG-4 Advanced Video Coding(AVC) and H.265/HEVC standards. Since H.262, the video coding standardsare based on the hybrid video coding structure wherein temporalprediction plus transform coding are utilized. To explore the futurevideo coding technologies beyond HEVC, the Joint Video Exploration Team(WET) was founded by video coding experts group (VCEG) and movingpictures experts group (MPEG) jointly in 2015. Since then, many newmethods have been adopted by JVET and put into the reference softwarenamed Joint Exploration Model (JEM). The JVET meeting is concurrentlyheld once every quarter, and the new coding standard is targeting at 50%bitrate reduction as compared to HEVC. The new video coding standard wasofficially named as Versatile Video Coding (VVC) in the April 2018 JVETmeeting, and the first version of VVC test model (VTM) was released atthat time. As there are continuous effort contributing to VVCstandardization, new coding techniques are being adopted to the VVCstandard in every JVET meeting. The VVC working draft and test model VTMare then updated after every meeting. The VVC project is now aiming fortechnical completion (FDIS) at the July 2020 meeting.

3.1. Picture Partitioning Schemes in HEVC

HEVC includes four different picture partitioning schemes, namelyregular slices, dependent slices, tiles, and Wavefront ParallelProcessing (WPP), which may be applied for Maximum Transfer Unit (MTU)size matching, parallel processing, and reduced end-to-end delay.

Regular slices are similar as in H.264/AVC. Each regular slice isencapsulated in its own NAL unit, and in-picture prediction (intrasample prediction, motion information prediction, coding modeprediction) and entropy coding dependency across slice boundaries aredisabled. Thus, a regular slice can be reconstructed independently fromother regular slices within the same picture (though there may stillhave interdependencies due to loop filtering operations).

The regular slice is the only tool that can be used for parallelizationthat is also available, in virtually identical form, in H.264/AVC.Regular slices based parallelization may not require muchinter-processor or inter-core communication (except for inter-processoror inter-core data sharing for motion compensation when decoding apredictively coded picture, which is typically much heavier thaninter-processor or inter-core data sharing due to in-pictureprediction). However, for the same reason, the use of regular slices canincur substantial coding overhead due to the bit cost of the sliceheader and due to the lack of prediction across the slice boundaries.Further, regular slices (in contrast to the other tools mentioned below)also serve as the key mechanism for bitstream partitioning to match MTUsize requirements, due to the in-picture independence of regular slicesand that each regular slice is encapsulated in its own NAL unit. In manycases, the goal of parallelization and the goal of MTU size matchingplace contradicting demands to the slice layout in a picture. Therealization of this situation led to the development of theparallelization tools mentioned below.

Dependent slices have short slice headers and allow partitioning of thebitstream at treeblock boundaries without breaking any in-pictureprediction. Basically, dependent slices provide fragmentation of regularslices into multiple NAL units, to provide reduced end-to-end delay byallowing a part of a regular slice to be sent out before the encoding ofthe entire regular slice is finished.

In WPP, the picture is partitioned into single rows of coding treeblocks (CTBs). Entropy decoding and prediction are allowed to use datafrom CTBs in other partitions. Parallel processing is possible throughparallel decoding of CTB rows, where the start of the decoding of a CTBrow is delayed by two CTBs, so to ensure that data related to a CTBabove and to the right of the subject CTB is available before thesubject CTB is being decoded. Using this staggered start (which appearslike a wavefront when represented graphically), parallelization ispossible with up to as many processors/cores as the picture contains CTBrows. Because in-picture prediction between neighboring treeblock rowswithin a picture is permitted, the inter-processor/inter-corecommunication to enable in-picture prediction can be substantial. TheWPP partitioning may not result in the production of additional NALunits compared to when it is not applied, thus WPP is not a tool for MTUsize matching. However, if MTU size matching may be required, regularslices can be used with WPP, with certain coding overhead.

Tiles define horizontal and vertical boundaries that partition a pictureinto tile columns and rows. Tile column runs from the top of a pictureto the bottom of the picture. Likewise, tile row runs from the left ofthe picture to the right of the picture. The number of tiles in apicture can be derived simply as number of tile columns multiply bynumber of tile rows.

The scan order of CTBs is changed to be local within a tile (in theorder of a CTB raster scan of a tile), before decoding the top-left CTBof the next tile in the order of tile raster scan of a picture. Similarto regular slices, tiles break in-picture prediction dependencies aswell as entropy decoding dependencies. However, they may not need to beincluded into individual NAL units (same as WPP in this regard); hencetiles may not be used for MTU size matching. Each tile can be processedby one processor/core, and the inter-processor/inter-core communicationfor in-picture prediction between processing units decoding neighboringtiles is limited to conveying the shared slice header in cases a sliceis spanning more than one tile, and loop filtering related sharing ofreconstructed samples and metadata. When more than one tile or WPPsegment is included in a slice, the entry point byte offset for eachtile or WPP segment other than the first one in the slice is signalledin the slice header.

For simplicity, restrictions on the application of the four differentpicture partitioning schemes have been specified in HEVC. A given codedvideo sequence may not include both tiles and wavefronts for most of theprofiles specified in HEVC. For each slice and tile, either or both ofthe following conditions may be fulfilled: 1) all coded treeblocks in aslice belong to the same tile; 2) all coded treeblocks in a tile belongto the same slice. Finally, a wavefront segment contains exactly one CTBrow, and when WPP is in use, if a slice starts within a CTB row, it mayend in the same CTB row.

A recent amendment to HEVC is specified in the JCT-VC output documentJCTVC-AC1005, J. Boyce, A. Ramasubramonian, R. Skupin, G. J. Sullivan,A. Tourapis, Y.-K. Wang (editors), “HEVC Additional SupplementalEnhancement Information (Draft 4),” Oct. 24, 2017, publicly availableherein:http://phenix.int-evry.fr/jct/doc_end_user/documents/29_Macau/wg11/JCTVC-AC1005-v2.zip.With this amendment included, HEVC specifies three MCTS-related SEImessages, namely temporal MCTSs SEI message, MCTSs extractioninformation set SEI message, and MCTSs extraction information nestingSEI message.

The temporal MCTSs SEI message indicates existence of MCTSs in thebitstream and signals the MCTSs. For each MCTS, motion vectors arerestricted to point to full-sample locations inside the MCTS and tofractional-sample locations that may use only full-sample locationsinside the MCTS for interpolation, and the usage of motion vectorcandidates for temporal motion vector prediction derived from blocksoutside the MCTS is disallowed. This way, each MCTS may be independentlydecoded without the existence of tiles not included in the MCTS.

The MCTSs extraction information sets SEI message provides supplementalinformation that can be used in the MCTS sub-bitstream extraction(specified as part of the semantics of the SEI message) to generate aconforming bitstream for an MCTS set. The information consists of anumber of extraction information sets, each defining a number of MCTSsets and containing RBSP bytes of the replacement VPSs, SPSs, and PPSsto be used during the MCTS sub-bitstream extraction process. Whenextracting a sub-bitstream according to the MCTS sub-bitstreamextraction process, parameter sets (VPSs, SPSs, and PPSs) may berewritten or replaced, slice headers may be slightly updated because oneor all of the slice address related syntax elements (includingfirst_slice_segment_in_pic_flag and slice_segment_address) typically mayhave different values.

3.2. Partitioning of Pictures in VVC

In VVC, A picture is divided into one or more tile rows and one or moretile columns. A tile is a sequence of CTUs that covers a rectangularregion of a picture. The CTUs in a tile are scanned in raster scan orderwithin that tile.

A slice consists of an integer number of complete tiles or an integernumber of consecutive complete CTU rows within a tile of a picture.

Two modes of slices are supported, namely the raster-scan slice mode andthe rectangular slice mode. In the raster-scan slice mode, a slicecontains a sequence of complete tiles in a tile raster scan of apicture. In the rectangular slice mode, a slice contains either a numberof complete tiles that collectively form a rectangular region of thepicture or a number of consecutive complete CTU rows of one tile thatcollectively form a rectangular region of the picture. Tiles within arectangular slice are scanned in tile raster scan order within therectangular region corresponding to that slice.

A subpicture contains one or more slices that collectively cover arectangular region of a picture.

FIG. 1 shows an example of raster-scan slice partitioning of a picture,where the picture is divided into 12 tiles and 3 raster-scan slices.

FIG. 2 shows an example of rectangular slice partitioning of a picture,where the picture is divided into 24 tiles (6 tile columns and 4 tilerows) and 9 rectangular slices.

FIG. 3 shows an example of a picture partitioned into tiles andrectangular slices, where the picture is divided into 4 tiles (2 tilecolumns and 2 tile rows) and 4 rectangular slices.

FIG. 4 shows an example of subpicture partitioning of a picture, where apicture is partitioned into 18 tiles, 12 on the left-hand side eachcovering one slice of 4 by 4 CTUs and 6 tiles on the right-hand sideeach covering 2 vertically-stacked slices of 2 by 2 CTUs, altogetherresulting in 24 slices and 24 subpictures of varying dimensions (eachslice is a subpicture).

3.3. Signalling of Subpictures, Tiles, and Slices in VVC

In the latest VVC draft text, information of subpictures, includessubpicture layout (i.e., the number of subpictures for each picture andthe position and size of each picture) and other sequence-levelsubpicture information, is signalled in the SPS. The order ofsubpictures signalled in the SPS defines the subpicture index. A list ofsubpicture IDs, one for each subpicture, may be explicitly signalled,e.g., in the SPS or in the PPS.

Tiles in VVC are conceptually the same as in HEVC, i.e., each picture ispartitioned into tile columns and tile rows, but with different syntaxin the PPS for signalling of tiles.

In VVC, the slice mode is also signalled in the PPS. When the slice modeis the rectangular slice mode, the slice layout (i.e., the number ofslices for each picture and the position and size of each slice) foreach picture is signalled in the PPS. The order of the rectangularslices within a picture signalled in the PPS defines the picture-levelslice index. The subpicture-level slice index is defined as the order ofthe slices within a subpicture in increasing order of the picture-levelslice indices. The positions and sizes of the rectangular slices aresignalled/derived based on either the subpicture positions and sizesthat are signalled in the SPS (when each subpicture contains only oneslice), or based on the tile positions and sizes that are signalled inthe PPS (when a subpicture may contain more than one slice). When theslice mode is the raster-scan slice mode, similarly as in HEVC, thelayout of slices within a picture is signalled in the slices themselves,with different details.

The SPS, PPS, and slice header syntax and semantics in the latest VVCdraft text that are most relevant to the inventions herein are asfollows.

7.3.2.3 Sequence Parameter Set RBSP Syntax

Descriptor seq_parameter_set_rbsp( ) {  ...  subpics_present_flag u(1) if( subpics_present_flag) {   sps_num_subpics_minus1 u(8)    for( i =0; i <= sps_num_subpics_minusl; i++ ) {    subpic_ctu_top_left_x[ i ]u(v)    subpic_ctu_top_left_y[ i ] u(v)    subpic_width_minus1[ i ] u(v)   subpic_height_minus1[ i ] u(v)    subpic_treated_as_pic_flag[ i ]u(1)    loop_filter_across_subpic_enabled_flag[ i ] u(1)   }  } sps_subpic_id_present_flag u(1)  if( sps_subpics_id_present_flag ) {  sps_subpic_id_signalling_present_flag U(1)   if(sps_subpics_id_signalling_present_flag ) {    sps_subpic_id_len_minus1ue(v)    for( i = 0; i <= sps_num_subpics_minus1; i++ )   sps_subpic_id[ i ] u(v)   }  }  ... }

7.4.3.3 Sequence Parameter Set RBSP Semantics

. . .

subpics_present_flag equal to 1 specifies that subpicture parameters arepresent in the SPS RBSP syntax. subpics_present_flag equal to 0specifies that subpicture parameters are not present in the SPS RBSPsyntax.

-   -   NOTE 2—When a bitstream is the result of a sub-bitstream        extraction process and contains only a subset of the subpictures        of the input bitstream to the sub-bitstream extraction process,        the value of subpics_present_flag may be set equal to 1 in the        RBSP of the SPSs.

sps_num_subpics_minus1 plus 1 specifies the number of subpictures.sps_num_subpics_minus1 may be in the range of 0 to 254. When notpresent, the value of sps_num_subpics_minus1 is inferred to be equal to0.

subpic_ctu_top_left_x[i] specifies horizontal position of top left CTUof i-th subpicture in unit of CtbSizeY. The length of the syntax elementis Ceil(Log2(pic_width_max_in_luma_samples/CtbSizeY)) bits. When notpresent, the value of subpic_ctu_top_left_x[i] is inferred to be equalto 0.

subpic_ctu_top_left_y[i] specifies vertical position of top left CTU ofi-th subpicture in unit of CtbSizeY. The length of the syntax element isCeil(Log2(pic_height_max_in_luma_samples/CtbSizeY)) bits. When notpresent, the value of subpic_ctu_top_left_y[i] is inferred to be equalto 0.

subpic_width_minus1[i] plus 1 specifies the width of the i-th subpicturein units of CtbSizeY. The length of the syntax element isCeil(Log2(pic_width_max_in_luma_samples/CtbSizeY)) bits. When notpresent, the value of subpic_width_minus1[i]is inferred to be equal toCeil(pic_width_max_in_luma_samples/CtbSizeY)−1.

subpic_height_minus1[i] plus 1 specifies the height of the i-thsubpicture in units of CtbSizeY. The length of the syntax element isCeil(Log2(pic_height_max_in_luma_samples/CtbSizeY)) bits. When notpresent, the value of subpic_height_minus1[i] is inferred to be equal toCeil(pic_height_max_in_luma_samples/CtbSizeY)−1.

subpic_treated_as_pic_flag[i] equal to 1 specifies that the i-thsubpicture of each coded picture in the CLVS is treated as a picture inthe decoding process excluding in-loop filtering operations.subpic_treated_as_pic_flag[i] equal to 0 specifies that the i-thsubpicture of each coded picture in the CLVS is not treated as a picturein the decoding process excluding in-loop filtering operations. When notpresent, the value of subpic_treated_as_pic_flag[i] is inferred to beequal to 0.

loop_filter_across_subpic_enabled_flag[i] equal to 1 specifies thatin-loop filtering operations may be performed across the boundaries ofthe i-th subpicture in each coded picture in the CLVS.loop_filter_across_subpic_enabled_flag[i] equal to 0 specifies thatin-loop filtering operations are not performed across the boundaries ofthe i-th subpicture in each coded picture in the CLVS. When not present,the value of loop_filter_across_subpic_enabled_pic_flag[i] is inferredto be equal to 1.

The following constraints may apply in bitstream conformance:

-   -   For any two subpictures subpicA and subpicB, when the subpicture        index of subpicA is less than that of subpicB, any coded slice        NAL unit of subPicA may precede any coded slice NAL unit of        subPicB in decoding order.    -   The shapes of the subpictures may be such that each subpicture,        when decoded, may have its entire left boundary and entire top        boundary consisting of picture boundaries or consisting of        boundaries of previously decoded subpictures.

sps_subpic_id_present_flag equal to 1 specifies that subpicture IDmapping is present in the SPS. sps_subpic_id_present_flag equal to 0specifies that subpicture ID mapping is not present in the SPS.

sps_subpic_id_signalling_present_flag equal to 1 specifies thatsubpicture ID mapping is signalled in the SPS.sps_subpic_id_signalling_present_flag equal to 0 specifies thatsubpicture ID mapping is not signalled in the SPS. When not present, thevalue of sps_subpic_id_signalling_present_flag is inferred to be equalto 0.

sps_subpic_id_len_minus1 plus1 specifies the number of bits used torepresent the syntax element sps_subpic_id[i]. The value ofsps_subpic_id_len_minus1 may be in the range of 0 to 15, inclusive.

sps_subpic_id[i] specifies that subpicture ID of the i-th subpicture.The length of the sps_subpic_id[i] syntax element issps_subpic_id_len_minus1+1 bits. When not present, and whensps_subpic_id_present_flag equal to 0, the value of sps_subpic_id[i] isinferred to be equal to i, for each i in the range of 0 tosps_num_subpics_minus1, inclusive

. . .

7.3.2.4 Picture Parameter Set RBSP Syntax

Descriptor pic_parameter_set_rbsp( ) {  ... mixed_nalu_types_in_pic_flag u(1) pps_subpic_id_signalling_present_flag u(1)  if(pps_subpics_id_signalling_present flag ) {   pps_num_subpics_minus1ue(v)   pps_subpic_id_len_minus1 ue(v)   for( i = 0; i <=pps_num_subpic_minus1; i++ )    pps_subpic_id[ i ] u(v)  } no_pic_partition_flag u(1)  if( !no_pic_partition_flag ) {  pps_log2_ctu_size_minus5 u(2)   num_exp_tile_columns_minus1 ue(v)  num_exp_tile_rows_minus1 ue(v)   for( i = 0; i <= num exp tile columnsminus1; i++)    tile_column_width_minusl[ i ] ue(v)   for( i = 0; i <=num_exp_tile_rows_minus1; i++)    tile_row_height_minus1[ i ] ue(v)  rect_slice_flag u(1)   if( rect_slice_flag )   single_slice_per_subpic_flag u(1)   if( rect_slice_flag &&!single_slice_per_subpic_flag ) {    num_slices_in_pic_minus1 ue(v)   tile_idx_delta_present_flag u(1)    for( i = 0; i <num_slices_in_pic_minus1; i++ ) {     slice_width_in_tiles_minus1[ i ]ue(v)     slice_height_in_tiles_minus1[ i ] ue(v)     if(slice_width_in_tiles_minusl[ i ] = = 0 &&     slice_height_in_tiles_minus1[ i ] = = 0 {    num_slices_in_tile_minus1[ i ] ue(v)     numSlicesInTileMinus1 =num_slices_in_tile_minus1[ i ]     for( j = 0; j <numSlicesInTileMinusl; j++ )      slice_height_in_ctu_minus1[ i++ ]ue(v)    }    if( tile_idx_delta_present_flag && i <num_slices_in_pic_minus1 )     tile_idx_delta[ i ] se(v)    }   }  loop_filter_across_tiles_enabled_flag u(1)  loop_filter_across_slices_enabled_flag u(1)  }  ... u(1) }

7.4.3.4 Picture Parameter Set RBSP Semantics

. . .

pps_subpic_id_signalling_present_flag equal to 1 specifies thatsubpicture ID mapping is signalled in the PPS.pps_subpic_id_signalling_present_flag equal to 0 specifies thatsubpicture ID mapping is not signalled in the PPS. Whensps_subpic_id_present_flag is 0 or sps_subpic_id_signalling_present_flagis equal to 1, pps_subpic_id_signalling_present_flag may be equal to 0.

pps_num_subpics_minus1 plus 1 specifies the number of subpictures in thecoded pictures referring to the PPS.

The value of pps_num_subpic_minus1 may be equal tosps_num_subpics_minus1.

pps_subpic_id_len_minus1 plus 1 specifies the number of bits used torepresent the syntax element pps_subpic_id[i]. The value ofpps_subpic_id_len_minus1 may be in the range of 0 to 15, inclusive.

The value of pps_subpic_id_len_minus1 may be the same for all PPSs thatare referred to by coded pictures in a CLVS.

pps_subpic_id[i] specifies the subpicture ID of the i-th subpicture. Thelength of the pps_subpic_id[i] syntax element ispps_subpic_id_len_minus1+1 bits.

no_pic_partition_flag equal to 1 specifies that no picture partitioningapplied to each picture referring to the PPS. no_pic_partition_flagequal to 0 specifies each picture referring to the PPS may bepartitioned into more than one tile or slice.

The value of no_pic_partition_flag may be the same for all PPSs that arereferred to by coded pictures within a CLVS.

The value of no_pic_partition_flag may not be equal to 1 when the valueof sps_num_subpics_minus1+1 is greater than 1.

pps_log2_ctu_size_minus5 plus 5 specifies the luma coding tree blocksize of each CTU. pps_log2_ctu_size_minus5 may be equal tosps_log2_ctu_size_minus5.

num_exp_tile_columns_minus1 plus 1 specifies the number of explicitlyprovided tile column widths. The value of num_exp_tile_columns_minus1may be in the range of 0 to PicWidthInCtbsY−1, inclusive. Whenno_pic_partition_flag is equal to 1, the value ofnum_exp_tile_columns_minus1 is inferred to be equal to 0.

num_exp_tile_rows_minus1 plus 1 specifies the number of explicitlyprovided tile row heights. The value of num_exp_tile_rows_minus1 may bein the range of 0 to PicHeightInCtbsY−1, inclusive. Whenno_pic_partition_flag is equal to 1, the value of num_tile_rows_minus1is inferred to be equal to 0.

tile_column_width_minus1[i] plus 1 specifies the width of the i-th tilecolumn in units of CTBs for i in the range of 0 tonum_exp_tile_columns_minus1−1, inclusive.tile_column_width_minus1[num_exp_tile_columns_minus1] is used to derivethe width of the tile columns with index greater than or equal tonum_exp_tile_columns_minus1 as specified in clause 6.5.1. When notpresent, the value of tile_column_width_minus1[0] is inferred to beequal to PicWidthInCtbsY−1.

tile_row_height_minus1[i] plus 1 specifies the height of the i-th tilerow in units of CTBs for i in the range of 0 tonum_exp_tile_rows_minus1−1, inclusive.tile_row_height_minus1[num_exp_tile_rows_minus1] is used to derive theheight of the tile rows with index greater than or equal tonum_exp_tile_rows_minus1 as specified in clause 6.5.1. When not present,the value of tile_row_height_minus1 [0] is inferred to be equal toPicHeightInCtbsY&31 1.

rect_slice_flag equal to 0 specifies that tiles within each slice are inraster scan order and the slice information is not signalled in PPS.rect_slice_flag equal to 1 specifies that tiles within each slice covera rectangular region of the picture and the slice information issignalled in the PPS. When not present, rect_slice_flag is inferred tobe equal to 1. When subpics_present_flag is equal to 1, the value ofrect_slice_flag may be equal to 1.

single_slice_per_subpic_flag equal to 1 specifies that each subpictureconsists of one and only one rectangular slice.single_slice_per_subpic_flag equal to 0 specifies that each subpicturemay consist of one or more rectangular slices. When subpics_present_flagis equal to 0, single_slice_per_subpic_flag may be equal to 0. Whensingle_slice_per_subpic_flag is equal to 1, num_slices_in_pic_minus1 isinferred to be equal to sps_num_subpics_minus1.

num_slices_in_pic_minus1 plus 1 specifies the number of rectangularslices in each picture referring to the PPS. The value ofnum_slices_in_pic_minus1 may be in the range of 0 toMaxSlicesPerPicture−1, inclusive, where MaxSlicesPerPicture is specifiedin Annex A. When no_pic_partition_flag is equal to 1, the value ofnum_slices_in_pic_minus1 is inferred to be equal to 0.

tile_idx_delta_present_flag equal to 0 specifies that tile_idx_deltavalues are not present in the PPS and that all rectangular slices inpictures referring to the PPS are specified in raster order according tothe process defined in clause 6.5.1. tile_idx_delta_present_flag equalto 1 specifies that tile_idx_delta values may be present in the PPS andthat all rectangular slices in pictures referring to the PPS arespecified in the order indicated by the values of tile_idx_delta.

slice_width_in_tiles_minus1[i] plus 1 specifies the width of the i-threctangular slice in units of tile columns. The value ofslice_width_in_tiles_minus1[i] may be in the range of 0 toNumTileColumns−1, inclusive. When not present, the value ofslice_width_in_tiles_minus1[i] is inferred as specified in clause 6.5.1.

slice_height_in_tiles_minus1[i] plus 1 specifies the height of the i-threctangular slice in units of tile rows. The value ofslice_height_in_tiles_minus1[i] may be in the range of 0 toNumTileRows−1, inclusive. When not present, the value ofslice_height_in_tiles_minus1[i] is inferred as specified in clause6.5.1.

num_slices_in_tile_minus1[i] plus 1 specifies the number of slices inthe current tile for the case where the i-th slice contains a subset ofCTU rows from a single tile. The value of num_slices_in_tile_minus1[i]may be in the range of 0 to RowHeight[tileY]−1, inclusive, where tileYis the tile row index containing the i-th slice. When not present, thevalue of num_slices_in_tile_minus1[i] is inferred to be equal to 0.

slice_height_in_ctu_minus1[i] plus 1 specifies the height of the i-threctangular slice in units of CTU rows for the case where the i-th slicecontains a subset of CTU rows from a single tile. The value ofslice_height_in_ctu_minus1[i] may be in the range of 0 toRowHeight[tileY]−1, inclusive, where tileY is the tile row indexcontaining the i-th slice.

tile_idx_delta[i] specifies the difference in tile index between thei-th rectangular slice and the (i+1)-th rectangular slice. The value oftile_idx_delta[i] may be in the range of −NumTilesInPic+1 toNumTilesInPic−1, inclusive. When not present, the value oftile_idx_delta[i] is inferred to be equal to 0. In all other cases, thevalue of tile_idx_delta[i] may not be equal to 0.

loop_filter_across_tiles_enabled_flag equal to 1 specifies that in-loopfiltering operations may be performed across tile boundaries in picturesreferring to the PPS. loop_filter_across_tiles_enabled_flag equal to 0specifies that in-loop filtering operations are not performed acrosstile boundaries in pictures referring to the PPS. The in-loop filteringoperations include the deblocking filter, sample adaptive offset filter,and adaptive loop filter operations. When not present, the value ofloop_filter_across_tiles_enabled_flag is inferred to be equal to 1.

loop_filter_across_slices_enabled_flag equal to 1 specifies that in-loopfiltering operations may be performed across slice boundaries inpictures referring to the PPS. loop_filter_across_slice_enabled_flagequal to 0 specifies that in-loop filtering operations are not performedacross slice boundaries in pictures referring to the PPS. The in-loopfiltering operations include the deblocking filter, sample adaptiveoffset filter, and adaptive loop filter operations. When not present,the value of loop_filter_across_slices_enabled_flag is inferred to beequal to 0.

7.3.7.1 General Slice Header Syntax

Descriptor slice_header( ) {  ...  if( subpics_present_flag)  slice_subpic_id u(v)  if( rect_slice_flag | | NumTilesInPic > 1 )  slice_address u(v)  if( !rect_slice_flag && NumTilesInPic > 1 )  num_tiles_in_slice_minus1 ue(v)  slice_type ue(v) ... }

7.4.8.1 General Slice Header Semantics

. . .

slice_subpic_id specifies the subpicture identifier of the subpicturethat contains the slice. If slice_subpic_id is present, the value of thevariable SubPicIdx is derived to be such that SubpicIdList[SubPicIdx] isequal to slice_subpic_id. Otherwise (slice_subpic_id is not present),the variable SubPicIdx is derived to be equal to 0. The length ofslice_subpic_id, in bits, is derived as follows:

-   -   If sps_subpic_id signalling_present_flag is equal to 1, the        length of slice_subpic_id is equal to        sps_subpic_id_len_minus1+1.    -   Otherwise, if ph_subpic_id_signalling_present_flag is equal to        1, the length of slice_subpic_id is equal to        ph_subpic_id_len_minus1+1.    -   Otherwise, if pps_subpic_id_signalling_present_flag is equal to        1, the length of slice_subpic_id is equal to        pps_subpic_id_len_minus1+1.    -   Otherwise, the length of slice_subpic_id is equal to Ceil(Log2        (sps_num_subpics_minus1+1)).

slice_address specifies the slice address of the slice. When notpresent, the value of slice_address is inferred to be equal to 0.

If rect_slice_flag is equal to 0, the following applies:

-   -   The slice address is the raster scan tile index.    -   The length of slice_address is Ceil(Log2 (NumTilesInPic)) bits.    -   The value of slice_address may be in the range of 0 to        NumTilesInPic−1, inclusive.

Otherwise (rect_slice_flag is equal to 1), the following applies:

-   -   The slice address is the slice index of the slice within the        SubPicIdx-th subpicture.    -   The length of slice_address is        Ceil(Log2(NumSlicesInSubpic[SubPicIdx])) bits.    -   The value of slice_address may be in the range of 0 to        NumSlicesInSubpic[SubPicIdx]−1, inclusive.

The following constraints may apply in bitstream conformance:

-   -   If rect_slice_flag is equal to 0 or subpics_present_flag is        equal to 0, the value of slice_address may not be equal to the        value of slice_address of any other coded slice NAL unit of the        same coded picture.    -   Otherwise, the pair of slice_subpic_id and slice_address values        may not be equal to the pair of slice_subpic_id and        slice_address values of any other coded slice NAL unit of the        same coded picture.    -   When rect_slice_flag is equal to 0, the slices of a picture may        be in increasing order of their slice address values.    -   The shapes of the slices of a picture may be such that each CTU,        when decoded, may have its entire left boundary and entire top        boundary consisting of a picture boundary or consisting of        boundaries of previously decoded CTU(s).

num_tiles_in_slice_minus1 plus 1, when present, specifies the number oftiles in the slice. The value of num_tiles_in_slice_minus1 may be in therange of 0 to NumTilesInPic−1, inclusive. The variableNumCtuInCurrSlice, which specifies the number of CTUs in the currentslice, and the list CtbAddrInCurrSlice[i], for i ranging from 0 toNumCtuInCurrSlice−1, inclusive, specifying the picture raster scanaddress of the i-th CTB within the slice, are derived as follows:

if(      rect_slice_flag      )      {  picLevelSliceIdx   =  SliceSubpicToPicIdx[ SubPicIdx ][ slice address ]  NumCtuInCurrSlice   =    NumCtuInSlice[ picLevelSliceIdx ]  for(   i   =   0;   i   <  NumCtuInCurrSlice;   i++   )   CtbAddrInCurrSlice[ i ] = CtbAddrInSlice[picLevelSliceIdx ][ i ]   (115) }         else         { NumCtuInCurrSlice        =        0 for(  tileIdx  =  sliceaddress;  tileIdx  <= slice_address +num_tiles_in_slice_minus1[ i ];  tileIdx++  )  {  tileX   =   tileIdx   %   NumTileColumns  tileY   =   tileIdx   /   NumTileColumns    for( ctbY = tileRowBd[tileY ]; ctbY < tileRowBd[ tileY + 1 ]; ctbY++ ) {    for( ctbX =tileColBd[ tileX ]; ctbX < tileColBd[ tileX + 1 ]; ctbX++ ) {    CtbAddrInCurrSlice[ NumCtuInCurrSlice ] = ctbY * PicWidthInCtb +ctbX     NumCtuInCurrSlice++    }   }  } }The variables SubPicLeftBoundaryPos, SubPicTopBoundaryPos,SubPicRightBoundaryPos, and SubPicBotBoundaryPos are derived as follows:

 if(   subpic_treated_as_pic_flag[ SubPicIdx ]   )   {  SubPicLeftBoundaryPos = subpic_ctu_top_left_x[ SubPicIdx ] * CtbSizeY  SubPicRightBoundaryPos = Min( pic_width_max_in_luma_samples − 1,   (subpic_ctu_top_left_x[ SubPicIdx ] + subpic_width_minus1[ SubPicIdx ] +1 ) * Ct  bSizeY − 1)   SubPicTopBoundaryPos = subpic_ctu_top_left_y[SubPicIdx ] *CtbSizeY (116)   SubPicBotBoundaryPos = Min(pic_height_max_in_luma_samples − 1,   ( subpic_ctu_top_left_y[ SubPicIdx] + subpic_height_minus1[ SubPicIdx ] + 1 ) * Ct  bSizeY − 1)  } ...

3.4. Embodiments from JVET-Q0075

Escape samples are employed to the handle the outlier case in thepalette mode.

The binarization of escape sample is 3^(rd) order Exp-Golumb (EG3) inthe current VTM. However, for a uniform distribution signal, the fixedlength binarization could be better than EG3 with both distortion andbitrate measurements.

JVET-Q0075 proposes to use the fixed length binarization for escapesamples and the quantization and dequantization process are alsomodified accordingly.

The maximal bit depth of an escape sample in the proposed method dependson the quantization parameter and derived as follows.

max (1, bitDepth−(max (QpPrimeTsMin, Qp)−4)/6)

Herein, the bitDepth is the internal bit depth, Qp is the currentquantization parameter (QP), QpPrimeTsMin is the minimal QP fortransform skip blocks and max is an operation to get a larger valuebetween two inputs.

Also, only a shifting operation may be used in the dequantizationprocess for an escape sample. Let escapeVal be the decoded escape valueand recon be the reconstructed value of an escape sample. The value isderived as follows.

shift=min (bitDepth−1, (max (QpPrimeTsMin, Qp)−4)/6)

recon=(escapeVal<<shift)

It is to guarantee that the distortion of the reconstructed value isalways smaller or equal to that of the current design, i.e.((escapeVal*levelScale [qP%6])<<(qP/6)+32)>>6.

At the encoder, the quantization is implemented as follows:

escapeVal=(p+(1<<(shift−1)))>>shift

escapeVal=clip3(0, (1<<bd)−1, escapeVal)

Compared with the current design using EG3 and quantization with adequantization table, one addition, one multiplication and two shiftingoperations, the proposed method is much simpler, which may involve justone shifting operation.

3.5. Embodiments from JVET-Q0294

In order to achieve efficient compression in mixed lossy and losslesscoding, JVET-Q0294 proposes to signal a flag at each coding tree unit(CTU) to indicate whether a CTU is coded as either in lossless or inlossy mode. If a CTU is lossless coded, an additional CTU level flag issignalled to specify the residual coding method, either regular residualcoding or transform skip residual coding, used for that CTU.

4. Examples of Technical Problems Solved by Solutions Herein

The existing designs for signalling of subpictures, tiles, and slices inVVC have the following problems:

-   -   1) The coding of sps_num_subpics_minus1 is u(8), which disallows        more than 256 subpictures per picture. However, in certain        applications, the maximum number of subpictures per picture may        be greater than 256.    -   2) It is allowed to have subpics_present_flag equal to 0 and        sps_subpic_id_present_flag equal to 1. However, this does not        make sense as subpics_present_flag equal to 0 means that the        CLVS has no information on subpictures at all.    -   3) A list of subpicture IDs may be signalled in picture headers        (PHs), one for each of the subpictures. However, when the list        of subpicture IDs is signalled in PHs, and when a subset of the        subpictures is extracted from the bitstream, all the PHs may be        changed. This is undesirable.    -   4) When subpicture IDs are indicated to be explicitly signalled,        by sps_subpic_id_present_flag (or the name of the syntax element        is changed to subpic_ids_explicitly_signalled_flag) equal to 1,        subpicture IDs may be not signalled anywhere. This is        problematic as subpicture IDs may be explicitly signalled in        either the SPS or the PPS when subpicture IDs are indicated to        be explicitly signalled.    -   5) When subpicture IDs are not explicitly signalled, the slice        header syntax element slice_subpic_id may still be signalled as        long as subpics_present_flag is equal to 1, including when        sps_num_subpics_minus1 is equal to 0. However, the length of        slice_subpic_id is specified as Ceil(Log2        (sps_num_subpics_minus1+1)) bits, which would be 0 bits when        sps_num_subpics_minus1 is equal to 0. This is problematic, as        the length of any present syntax elements may not be 0 bits.    -   6) The subpicture layout, including the number of subpictures        and their sizes and positions, keeps unchanging for the entire        CLVS. Even when the subpicture IDs are not explicitly signalled        in the SPS or the PPS, the subpicture ID length may still be        signalled, for the subpicture ID syntax element in slice        headers.    -   7) Whenever rect_slice_flag is equal to 1, the syntax element        slice_address is signalled in the slice header and specifies the        slice index within the subpicture containing the slice,        including when the number of slices within the subpicture (i.e.,        NumSlicesInSubpic[SubPicIdx]) is equal to 1. However, when        rect_slice_flag is equal to 1, the length of slice_address is        specified to be Ceil(Log2(NumSlicesInSubpic[SubPicIdx])) bits,        which would be 0 bits when NumSlicesInSubpic[SubPicIdx] is equal        to 1. This is problematic, as the length of any present syntax        elements may not be 0 bits.    -   8) There is redundancy between the syntax elements        no_pic_partition_flag and pps_num_subpics_minus1, although the        latest VVC text has the following constraint: When        sps_num_subpics_minus1 is greater than 0, the value of        no_pic_partition_flag may be equal to 1.    -   9) Within a CLVS, the subpicture ID value for a particular        subpicture position or index may change from picture to picture.        When this happens, in principle, the subpicture may not use        inter prediction by referring to a reference picture in the same        layer. However, there lacks a constraint to prohibit this in the        VVC specification.    -   10) In VVC design, a reference picture could be a picture in a        different layer to support multiple applications, e.g., scalable        video coding and multi-view video coding. If subpicture is        present in different layers, whether to allow or disallow the        inter-layer prediction should be studied.

5. Example Techniques and Embodiments

To solve the above problems, and others, methods as summarized below aredisclosed. The inventions should be considered as examples to explainthe general concepts and should not be interpreted in a narrow way.Furthermore, these inventions can be applied individually or combined inany manner.

The following abbreviations have the same meaning as they are inJVET-P1001-vE.

-   -   BP (buffering period), BP SEI (supplemental enhancement        information),    -   PT (picture timing), PT SEI,    -   AU (access unit),    -   OP (operation point),    -   DUI (decoding unit information), DUI SEI,    -   NAL (network abstraction layer),    -   NUT (NAL unit type),    -   GDR (gradual decoding refresh),    -   SLI (subpicture level information), SLI SEI

To solve the first problem, change the coding of sps_num_subpics_minus1from u(8) to ue(v), to enable more than 256 subpictures per picture.

-   -   a. Furthermore, the value of sps_num_subpics_minus1 is        restricted to be in the range of 0 to        Ceil(pic_width_max_in_luma_samples÷CtbSizeY)*Ceil(pic_height_max_in_luma_samples÷CtbSizeY)−1,        inclusive.    -   b. Furthermore, the number of subpictures per picture is further        restricted in the definition of levels.    -   2) To solve the second problem, condition the signalling of the        syntax element sps_subpic_id_present_flag on        “if(subpics_present_flag)”, i.e., the syntax element        sps_subpic_id_present_flag is not signalled when        subpics_present_flag is equal to 0, and infer the value of        sps_subpic_id_present_flag to be equal to 0 when it is not        present.        -   a. Alternatively, the syntax element            sps_subpic_id_present_flag is still signalled when            subpics_present_flag is equal to 0, but the value may be            equal to 0 when subpics_present_flag is equal to 0.        -   b. Furthermore, the names of the syntax elements            subpics_present_flag and sps_subpic_id_present_flag are            changed to be subpic_info_present_flag and            subpic_ids_explicitly_signalled_flag, respectively.    -   3) To solve the third problem, the signalling of subpicture IDs        in the PH syntax is removed. Consequently, the list        SubpicIdList[i], for i in the range of 0 to        sps_num_subpics_minus1, inclusive, is derived as follows:

for(  i  =  0;  i   <=   sps_num_subpics_minus1;  i++ )  if(    subpic_ids_explicitly_signalled_flag    )   SubpicIdList[ i ]  = subpic_ids_in_pps_flag  ?  pps_subpic_id[ i ] : sps_subpic_id[ i ] else   SubpicIdList[ i ] = i

-   -   4) To solve the fourth problem, subpicture IDs are signalled        either in the SPS or in the PPS when subpictures are indicated        to be explicitly signalled.        -   a. This is realized by adding the following constraint: If            subpic_ids_explicitly_signalled_flag is 0 or            subpic_ids_in_sps_flag is equal to 1, subpic_ids_in_pps_flag            may be equal to 0. Otherwise            (subpic_ids_explicitly_signalled_flag is 1 and            subpic_ids_in_sps_flag is equal to 0),            subpic_ids_in_pps_flag may be equal to 1.    -   5) To solve the fifth and sixth problems, the length of        subpicture IDs is signalled in the SPS regardless of the value        of the SPS flag sps_subpic_id_present_flag (or renamed to        subpic_ids_explicitly_signalled_flag), although the length may        also be signalled in the PPS when subpicture IDs are explicitly        signalled in the PPS to avoid parsing dependency of PPS on SPS.        In this case, the length also specifies the length of the        subpicture IDs in the slice headers, even subpicture IDs are not        explicitly signalled in the SPS or PPS. Consequently, the length        of the slice_subpic_id, when present, is also specified by the        subpicture ID length signalled in the SPS.    -   6) Alternatively, to solve the fifth and sixth problems, a flag        is added to the SPS syntax, the value of 1 for which to specify        the existence of the subpicture ID length in the SPS syntax.        This flag is present is independent of the value of the flag        indicating whether subpicture IDs are explicitly signalled in        the SPS or PPS. The value of this flag may be equal to either 1        or 0 when subpic_ids_explicitly_signalled_flag is equal to 0,        but the value of flag may be equal to 1 when        subpic_ids_explicitly_signalled_flag is equal to 1. When this        flag is equal to 0, i.e., the subpicture length is not present,        the length of slice_subpic_id is specified to be Max(Ceil(Log2        (sps_num_subpics_minus1+1)), 1) bits (as opposed to be Ceil(Log2        (sps_num_subpics_minus1+1)) bits in the latest VVC draft text).        -   a. Alternatively, this flag is present only when            subpic_ids_explicitly_signalled_flag is equal to 0, and when            subpic_ids_explicitly_signalled_flag is equal to 1 the value            of this flag is inferred to be equal to 1.    -   7) To solve the seventh problem, when rect_slice_flag is equal        to 1, the length of slice_address is specified to be        Max(Ceil(Log2(NumSlicesInSubpic[SubPicIdx]), 1) bits.        -   a. Alternatively, further more, when rect_slice_flag is            equal to 0, the length of slice_address is specified to            Max(Ceil(Log2 (NumTilesInPic)), 1) bits, as opposed to be            Ceil(Log2 (NumTilesInPic)) bits.    -   8) To solve the eighth problem, condition the signalling of        no_pic_partition_flag on “if(subpic_ids_in_pps_flag &&        pps_num_subpics_minus_1>0)”, and add the following inference:        When not present, the value of no_pic_partition_flag is inferred        to be equal to 1.        -   a. Alternatively, move the subpicture ID syntax (all the            four syntax elements) after the tile and slice syntax in the            PPS, e.g., immediately before the syntax element            entropy_coding_sync_enabled_flag, and then condition the            signalling of pps_num_subpics_minus1 on            “if(no_pic_partition_flag)”.    -   9) To solve the ninth problem, the following constraint is        specified: For each particular subpicture index (or        equivalently, subpicture position), when the subpicture ID value        changes at a picture picA compared to that in the previous        picture in decoding order in the same layer as picA, unless picA        is the first picture of the CLVS, the subpicture at picA may        only contain coded slice NAL units with nal_unit_type equal to        IDR_W_RADL, IDR_N_LP, or CRA_NUT.        -   a. Alternatively, the above constraint applies only for            subpicture indices for which the value of the            subpic_treated_as_pic_flag[i] is equal to 1.        -   b. Alternatively, for both item 9 and 9a, change            “IDR_W_RADL, IDR_N_LP, or CRA_NUT” to “IDR_W_RADL, IDR_N_LP,            CRA_NUT, RSV_IRAP_11, or RSV_IRAP_12”.        -   c. Alternatively, the subpicture at picA may contain other            types of coded slice NAL units, however, these coded slice            NAL units only use one or more of intra prediction, Intra            Block Copy (IBC) prediction, and palette mode prediction.

d. Alternatively, a first video unit (such as a slice, a tile, a block,etc.) in a subpicture of picA may refer to a second video unit in aprevious picture. It is constrained that the second video unit and thefirst video unit may be in subpictures with the same subpicture index,although the subpicture IDs of the two may be different. A subpictureindex is a unique number assigned to a subpicture, which may not bechanged in a CLVS.

10) For a particular subpicture index (or equivalently, subpictureposition), indications of which of subpictures, identified by layer IDvalues together with subpicture indices or subpicture ID values, areallowed to be used as reference pictures may be signalled in thebitstream.

-   -   11) For multiple-layer cases, when certain conditions (e.g.,        which may depend on the number of subpictures, location of        subpictures) are satisfied, inter-layer prediction (ILR) from a        subpicture in a different layer is allowed, while when the        certain conditions are not satisfied, ILR is disabled.        -   a. In one example, even when two subpictures in two layers            are with the same subpicture index value but different            subpicture ID values, the inter-layer prediction may be            still allowed when certain conditions are satisfied.            -   i. In one example, the certain conditions are “if the                two layers are associated with different view order                index/view order ID values”.        -   b. It may be constrained that a first subpicture in a first            layer and second subpicture in a second layer may be at the            collocated positions and/or rational width/height if the two            subpictures have the same subpicture index.        -   c. It may be constrained that a first subpicture in a first            layer and second subpicture in a second layer may be at the            collocated positions and/or rational width/height if the            first subpicture can refer to the second reference            subpicture.    -   12) An indication of whether a current subpicture may use        Inter-Layer Prediction (ILP) from sample values and/or other        values, e.g., motion information and/or coding modes        information, associated with regions or subpictures of reference        layers is signalled in the bitstream, such as in        VPS/DPS/SPS/PPS/APS/sequence header/picture header.        -   a. In one example, the reference regions or subpictures of            reference layers are the ones that contains at least one            collocated sample of a sample within the current subpicture.        -   b. In one example, the reference regions or subpictures of            reference layers are outside the collocated region of the            current subpicture.        -   c. In one example, such an indication is signalled in one or            more SEI messages.        -   d. In one example, such an indication is signalled            regardless of whether the reference layers have multiple            subpictures or not, and, when multiple subpictures are            present in one or more of the reference layers, regardless            of whether the partitioning of the pictures into subpictures            aligned with the current picture such that each subpicture            in the current picture a corresponding subpicture in a            reference picture that covers the collocated region, and            furthermore, regardless of whether the            corresponding/collocated subpicture has the same subpicture            ID value as the current subpicture.    -   13) When a BP SEI message and a PT SEI message that apply to a        particular OP are present within an AU, the BP SEI messages may        precede the PT SEI message in decoding order.    -   14) When a BP SEI message and a DUI SEI message that apply to a        particular OP are present within an AU, the BP SEI messages may        precede the DUI SEI message in decoding order.    -   15) When a PT SEI message and a DUI SEI message that apply to a        particular OP are present within an AU, the PT SEI messages may        precede the DUI SEI message in decoding order.    -   16) An indicator of whether a picture is an IRAP/GDR picture        flag is signalled at the beginning of the picture header, and        no_output_of_prior_pics_flag may be signalled conditioned on the        indicator.

An exemplary syntax design is as below:

Descriptor picture_header_rbsp( ) {  irap_or_gdr_pic_flag u(1) . . . if( irap_or_gdr_pic_flag )   no_output_of_prior_pics_flag u(1) . . .

irap_or_gdr_pic_flag equal to 1 specifies the picture associated withthe PH is an IRAP or GDR picture. irap_or_gdr_pic_flag equal to 0specifies the picture associated with the PH is neither an IRAP picturenor a GDR picture.

-   -   17) It is disallowed that a picture for which the value of        mixed_nalu_types_in_pic_flag equal to 0 may not contain a coded        slice NAL unit with nal_unit_type equal to GDR_NUT.    -   18) A syntax element (namely mixed_slice_types_in_pic_flag) is        signalled in the PPS. If mixed_slice_types_in_pic_flag is equal        to 0, the slice type (B, P, or I) is coded in the PH. Otherwise,        the slice type is coded in SHs. The syntax values related to the        unused slice types are further skipped in the picture header.        The syntax element mixed_slice_types_in_pic_flag is signalled        conditionally as follows:

if( !rect slice flag | | num slices in pic minus 1 > 0 )mixed_slice_types_in_pic_flag u(1)

-   -   19) In the SPS or PPS, signal up to N1 (e.g., 3) vertical        virtual boundaries and up to N2 (e.g., 3) horizontal virtual        boundaries. In the PH, signal up to N3 (e.g., 1) extra vertical        boundaries and up to N4 (e.g., 1) extra horizontal virtual        boundaries, and it is constrained that the total number of        vertical virtual boundaries may be less than or equal to N1, and        the total number of horizontal virtual boundaries may be less        than or equal to N2.    -   20) The syntax element inter_layer_ref_pics_present_flag in the        SPS may be signalled conditionally. For example as follows:

if( sps_video_parameter_set_id != 0) inter_layer_ref_pics_present_flagu(1)

-   -   21) Signal the syntax elements entropy_coding_sync_enabled_flag        and entry_point_offsets_present_flag in the SPS instead of in        the PPS.    -   22) The values of vps_num_ptls_minus1 and        num_ols_hrd_params_minus1 may be less than a value T. For        example, T may be equal to TotalNumOlss specified in        WET-2001-vE.        -   a. The difference between T and vps_num_ptls_minus1 or            (vps_num_ptls_minus1+1) may be signalled.        -   b. The difference between T and hrd_params_minus1 or            (hrd_params_minus1+1) may be signalled.        -   c. The above differences may be signalled by unary code or            Exponential Golomb code.    -   23) The value of vps_num_dpb_params_minus1 may be less than or        equal to vps_max_layers_minus1.        -   a. The difference between T and vps_num_ptls_minus1 or            (vps_num_ptls_minus1+1) may be signalled.        -   b. The difference may be signalled by unary code or            Exponential Golomb code.    -   24) It is allowed that an EOB NAL unit to be made available to        the decoder either by being included in the bitstream, or        provided through an external means.    -   25) It is allowed that the EOS NAL unit may be made available to        the decoder either by being included in the bitstream, or        provided through an external means.    -   26) For each layer with layer index i, when        vps_independent_layer_flag[i] is equal to 0, each picture in the        layer may contain only one subpicture.    -   27) In a sub-bitstream extraction process, specify that,        whenever a VCL NAL unit is removed, also remove the filler data        units that are associated with the VCL NAL units and also remove        all filler SEI messages in SEI NAL units that are associated        with the VCL NAL unit.    -   28) It is constrained that, when a SEI NAL unit contains a        filler SEI message, it may not contain any other SEI message        that is not a filler SEI message.        -   a. Alternatively, it is constrained that, when a SEI NAL            unit contains a filler SEI message, it may contain any other            SEI message.    -   29) It is constrained that a VCL NAL unit may have at most one        associated filler NAL unit.    -   30) It is constrained that a VCL NAL unit may have at most one        associated filler NAL unit.    -   31) It is proposed that a flag is signalled to indicate whether        a video unit is coded as either in lossless or in lossy mode,        wherein the video unit may be a CU or a CTU, and the signalling        of an escape sample in the palette mode may depend on the flag.        -   a. In one example, the binarization method of an escape            sample in the palette mode may depend on the flag.        -   b. In one example, the determination of the coding context            in arithmetic coding for an escape sample in the palette            mode may depend on the flag.

6. Embodiments

Below are some example embodiments for all the invention aspects exceptitem 8 summarized above in Section 5, which can be applied to the VVCspecification. The changed texts are based on the latest VVC text inJVET-P2001-v14. Most relevant parts that have been added or modified areshown in

and the most relevant removed parts are highlighted in enclosed inbolded double brackets, e.g., [[a]] indicates that “a” has been removed.There are some other changes that are editorial in nature and thus nothighlighted.

6.1. First Embodiment

7.3.2.3 Sequence Parameter Set RBSP Syntax

Descriptor seq_parameter_set_rbsp( ) {  ...  sps_log2_ctu_size_minus5u(2)  

 if(

 ) {   sps_num_sub_pics_minus1

  for( i = 0; i <= sps_num_subpics_minusl; i++ ) {   subpic_ctu_top_left_x[ i ] u(v)    subpic_ctu_top_left_y[ i ] u(v)   subpic_width_minus1[ i ] u(v)    subpic_height_minus1[ i ] u(v)   subpic_treated_as_pic_flag[ i ] u(1)   loop_filter_across_subpic_enabled _flag[ i ] u(1)   }   

  

u(1)   if(

 ) {   

u(1)    if(

 )     for( i = 0; i <= sps_num_subpics_minusl; i++ )     sps_subpic_id[ i ] u(v)   }  }  ... }

7.4.3.3 Sequence Parameter Set RBSP Semantics

-   -   NOTE 2—When a bitstream is the result of a sub-bitstream        extraction process and contains only a subset of the subpictures        of the input bitstream to the sub-bitstream extraction process,        the value of        may be set equal to 1 in the SPSs.

sps_num_subpics_minus1 plus 1 specifies the number of subpictures.

When not present, the value of sps_num_subpics_minus1 is inferred to beequal to 0.

subpic_ctu_top_left_x[i] specifies horizontal position of top left CTUof i-th subpicture in unit of CtbSizeY. The length of the syntax elementis Ceil(Log2(pic_width_max_in_luma_samples/CtbSizeY)) bits. When notpresent, the value of subpic_ctu_top_left_x[i] is inferred to be equalto 0.

subpic_ctu_top_left_y[i] specifies vertical position of top left CTU ofi-th subpicture in unit of CtbSizeY. The length of the syntax element isCeil(Log2(pic_height_max_in_luma_samples/CtbSizeY)) bits. When notpresent, the value of subpic_ctu_top_left_y[i] is inferred to be equalto 0.

subpic_width_minus1[i] plus 1 specifies the width of the i-th subpicturein units of CtbSizeY. The length of the syntax element isCeil(Log2(pic_width_max_in_luma_samples/CtbSizeY)) bits. When notpresent, the value of subpic_width_minus1[i] is inferred to be equal toCeil(pic_width_max_in_luma_samples/CtbSizeY)−1.

subpic_height_minus1[i] plus 1 specifies the height of the i-thsubpicture in units of CtbSizeY. The length of the syntax element isCeil(Log2(pic_height_max_in_luma_samples/CtbSizeY)) bits. When notpresent, the value of subpic_height_minus1[i] is inferred to be equal toCeil(pic_height_max_in_luma_samples/CtbSizeY)−1.

subpic_treated_as_pic_flag[i] equal to 1 specifies that the i-thsubpicture of each coded picture in the CLVS is treated as a picture inthe decoding process excluding in-loop filtering operations.subpic_treated_as_pic_flag[i] equal to 0 specifies that the i-thsubpicture of each coded picture in the CLVS is not treated as a picturein the decoding process excluding in-loop filtering operations. When notpresent, the value of subpic_treated_as_pic_flag[i] is inferred to beequal to 0.

loop_filter_across_subpic_enabled_flag[i] equal to 1 specifies thatin-loop filtering operations may be performed across the boundaries ofthe i-th subpicture in each coded picture in the CLVS.loop_filter_across_subpic_enabled_flag[i] equal to 0 specifies thatin-loop filtering operations are not performed across the boundaries ofthe i-th subpicture in each coded picture in the CLVS. When not present,the value of loop_filter_across_subpic_enabled_pic_flag[i] is inferredto be equal to 1.

The following constraints may apply in bitstream conformance:

-   -   For any two subpictures subpicA and subpicB, when the subpicture        index of subpicA is less than that of subpicB, any coded slice        NAL unit of subPicA may precede any coded slice NAL unit of        subPicB in decoding order.    -   The shapes of the subpictures may be such that each subpicture,        when decoded, may have its entire left boundary and entire top        boundary consisting of picture boundaries or consisting of        boundaries of previously decoded subpictures.

sps_subpic_id[i] specifies the subpicture ID of the i-th subpicture. Thelength of the sps_subpic_id[i] syntax element issps_subpic_id_len_minus1+1 bits.

7.3.2.4 Picture Parameter Set RBSP Syntax

Descriptor pic_parameter_set_rbsp( ) {  ... mixed_nalu_types_in_pic_flag u(1)  

u(1)  if(

 ) {   pps_num_subpics_minus1 ue(v)   pps_subpic_id_len_minus1 ue(v)  for( i = 0; i <= pps_num_subpic_minus1; i++ )   pps_subpic_id[ i ]u(v)  }  no_pic_partition_flag u(1)  if( !no_pic_partition_flag ) {  pps_log2_ctu_size_minus5 u(2)   num_exp_tile_columns_minus1 ue(v)  num_exp_tile_rows_minus1 ue(v)   for( i = 0; i <=num_exp_tile_columns_minus1; i++)    tile_column_width_minusl[ i ] ue(v)  for( i = 0; i <= num_exp_tile_rows_minus1; i++)   tile_row_height_minus1[ i ] ue(v)   if( NumTilesInPic > 1 )   rect_slice_flag u(1)   if( rect_slice_flag)   single_slice_per_subpic_flag u(1)   if( rect_slice_flag && ! singleslice_per_subpic_flag ) {   num_slices_in_pic_minus1 ue(v)  tile_idx_delta_present_flag u(1)   for( i = 0; i <num_slices_in_pic_minus1; i++ ) {    slice_width_in_tiles_minusl[ i ]ue(v)    slice_height_in_tiles_minusl[ i ] ue(v)    if(slice_width_in_tiles_minus1[ i ]== 0 &&      slice_height_in_tiles_minus1[ i ] = = 0 ) {    num_slices_in_tile_minus1[ i ] ue(v)     for( j = 0; j <num_slices_in_tile_minusl[ i ]; j++ )      slice_height_in_ctu_minusl[i++ ] ue(v)    }    if( tile_idx_delta_present_flag && i <num_slices_in_pic_minus1 )     tile_idx_delta[ i ] se(v)   }   }  loop_filter_across_tiles_enabled_flag u(1)  loop_filter_across_slices_enabled_flag u(1)  }  ... }

7.4.3.4 Picture Parameter Set RBSP Semantics

pps_num_subpics_minus1 may be equal to sps_num_subpics_minus1.

pps_subpic_id_len_minus1 may be equal to sps_subpic_id_len_minus1.

pps_subpic_id[i] specifies the subpicture ID of the i-th subpicture. Thelength of the

pps_subpic_id[i] syntax element is pps_subpic_id_len_minus1+1 bits.

In some cases, for any i and j in the range of 0 tosps_num_subpics_minus1, inclusive, when i is less than j,SubpicIdList[i] may be less than SubpicIdList[j].

. . .

rect_slice_flag equal to 0 specifies that tiles within each slice are inraster scan order and the slice information is not signalled in PPS.rect_slice_flag equal to 1 specifies that tiles within each slice covera rectangular region of the picture and the slice information issignalled in the PPS. When not present, rect_slice_flag is inferred tobe equal to 1.

αis equal to 1, the value of rect_slice_flag may be equal to 1.

single_slice_per_subpic_flag equal to 1 specifies that each subpictureconsists of one and only one rectangular slice.single_slice_per_subpic_flag equal to 0 specifies that each subpicturemay consist of one or more rectangular slices. When

is equal to 0, single_slice_per_subpic_flag may be equal to 0. Whensingle_slice_per_subpic_flag is equal to 1, num_slices_in_pic_minus1 isinferred to be equal to sps_num_subpics_minus1.

7.3.7.1 General Slice Header Syntax

Descriptor slice_header( ) {  ...  if(

 )   slice_subpic_id u(v)  if( rect_slice_flag | | NumTilesInPic > 1 )  slice_address u(v)  if( !rect_slice_flag && NumTilesInPic > 1 )  num_tiles_in_slice_minus1 ue(v)  slice_type ue(v) ... }

7.4.8.1 General Slice Header Semantics

. . .

slice_subpic_id specifies the subpicture ID of the subpicture thatcontains the slice.

When not present, the value of slice_subpic_id is inferred to be equalto 0.

The variable SubPicIdx is derived to be the value such thatSubpicIdList[SubPicIdx] is equal to slice_subpic_id.

slice_address specifies the slice address of the slice. When notpresent, the value of slice_address is inferred to be equal to 0.

If rect_slice_flag is equal to 0, the following applies:

-   -   The slice address is the raster scan tile index.    -   The length of slice_address is Ceil(Log2 (NumTilesInPic)) bits.    -   The value of slice_address may be in the range of 0 to        NumTilesInPic−1, inclusive.

Otherwise (rect_slice_flag is equal to 1), the following applies:

-   -   The slice address is the subpicture-level slice index of the        slice.    -   The length of slice_address is        bits.    -   The value of slice_address may be in the range of 0 to        NumSlicesInSubpic[SubPicIdx]−1, inclusive.

The following constraints may apply in bitstream conformance:

-   -   If rect_slice_flag is equal to 0 or        is equal to 0, the value of slice_address may not be equal to        the value of slice_address of any other coded slice NAL unit of        the same coded picture.    -   Otherwise, the pair of slice_subpic_id and slice_address values        may not be equal to the pair of slice_subpic_id and        slice_address values of any other coded slice NAL unit of the        same coded picture.    -   When rect_slice_flag is equal to 0, the slices of a picture may        be in increasing order of their slice address values.    -   The shapes of the slices of a picture may be such that each CTU,        when decoded, may have its entire left boundary and entire top        boundary consisting of a picture boundary or consisting of        boundaries of previously decoded CTU(s).

FIG. 5 is a block diagram showing an example video processing system 500in which various techniques disclosed herein may be implemented. Variousimplementations may include some or all of the components of the system500. The system 500 may include input 502 for receiving video content.The video content may be received in a raw or uncompressed format, e.g.,8 or 10 bit multi-component pixel values, or may be in a compressed orencoded format. The input 502 may represent a network interface, aperipheral bus interface, or a storage interface. Examples of networkinterface include wired interfaces such as Ethernet, passive opticalnetwork (PON), etc. and wireless interfaces such as Wi-Fi or cellularinterfaces.

The system 500 may include a coding component 504 that may implement thevarious coding or encoding methods described in the present document.The coding component 504 may reduce the average bitrate of video fromthe input 502 to the output of the coding component 504 to produce acoded representation of the video. The coding techniques are thereforesometimes called video compression or video transcoding techniques. Theoutput of the coding component 504 may be either stored, or transmittedvia a communication connected, as represented by the component 506. Thestored or communicated bitstream (or coded) representation of the videoreceived at the input 502 may be used by the component 508 forgenerating pixel values or displayable video that is sent to a displayinterface 510. The process of generating user-viewable video from thebitstream representation is sometimes called video decompression.Furthermore, while certain video processing operations are referred toas “coding” operations or tools, it will be appreciated that the codingtools or operations are used at an encoder and corresponding decodingtools or operations that reverse the results of the coding will beperformed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include serial advanced technology attachment (SATA),peripheral component interconnect (PCI), integrated drive electronics(IDE)interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

FIG. 6 is a block diagram of a video processing apparatus 600. Theapparatus 600 may be used to implement one or more of the methodsdescribed herein. The apparatus 600 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 600 may include one or more processors 602, one or morememories 604 and video processing hardware 606. The processor(s) 602 maybe configured to implement one or more methods described in the presentdocument. The memory (memories) 604 may be used for storing data andcode used for implementing the methods and techniques described herein.The video processing hardware 606 may be used to implement, in hardwarecircuitry, some techniques described in the present document. In someembodiments, the hardware 606 may be partly or entirely in theprocessors 602, e.g., a graphics processor.

FIG. 7 is a block diagram that illustrates an example video codingsystem 100 that may utilize the techniques of this disclosure.

As shown in FIG. 7, video coding system 100 may include a source device110 and a destination device 120. Source device 110 generates encodedvideo data which may be referred to as a video encoding device.Destination device 120 may decode the encoded video data generated bysource device 110 which may be referred to as a video decoding device.

Source device 110 may include a video source 112, a video encoder 114,and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, aninterface to receive video data from a video content provider, and/or acomputer graphics system for generating video data, or a combination ofsuch sources. The video data may comprise one or more pictures. Videoencoder 114 encodes the video data from video source 112 to generate abitstream. The bitstream may include a sequence of bits that form acoded representation of the video data. The bitstream may include codedpictures and associated data. The coded picture is a codedrepresentation of a picture. The associated data may include sequenceparameter sets, picture parameter sets, and other syntax structures. I/Ointerface 116 may include a modulator/demodulator (modem) and/or atransmitter. The encoded video data may be transmitted directly todestination device 120 via I/O interface 116 through network 130 a. Theencoded video data may also be stored onto a storage medium/server 130 bfor access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface126 may acquire encoded video data from the source device 110 or thestorage medium/server 130 b. Video decoder 124 may decode the encodedvideo data. Display device 122 may display the decoded video data to auser. Display device 122 may be integrated with the destination device120, or may be external to destination device 120 which be configured tointerface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard, Versatile Video Coding (VVM) standard and other current and/orfurther standards.

FIG. 8 is a block diagram illustrating an example of video encoder 200,which may be video encoder 114 in the system 100 illustrated in FIG. 7.

Video encoder 200 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 8, video encoder200 includes a plurality of functional components. The techniquesdescribed in this disclosure may be shared among the various componentsof video encoder 200. In some examples, a processor may be configured toperform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partitionunit 201, a predication unit 202 which may include a mode select unit203, a motion estimation unit 204, a motion compensation unit 205, anintra prediction unit 206, a residual generation unit 207, a transformunit 208, a quantization unit 209, an inverse quantization unit 210, aninverse transform unit 211, a reconstruction unit 212, a buffer 213, andan entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, ordifferent functional components. In an example, predication unit 202 mayinclude an intra block copy (IBC) unit. The IBC unit may performpredication in an IBC mode in which at least one reference picture is apicture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 andmotion compensation unit 205 may be highly integrated, but arerepresented in the example of FIG. 8 separately for purposes ofexplanation.

Partition unit 201 may partition a picture into one or more videoblocks. Video encoder 200 and video decoder 300 may support variousvideo block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter,e.g., based on error results, and provide the resulting intra- orinter-coded block to a residual generation unit 207 to generate residualblock data and to a reconstruction unit 212 to reconstruct the encodedblock for use as a reference picture. In some example, Mode select unit203 may select a combination of intra and inter predication (CIIP) modein which the predication is based on an inter predication signal and anintra predication signal. Mode select unit 203 may also select aresolution for a motion vector (e.g., a sub-pixel or integer pixelprecision) for the block in the case of inter-predication.

To perform inter prediction on a current video block, motion estimationunit 204 may generate motion information for the current video block bycomparing one or more reference frames from buffer 213 to the currentvideo block. Motion compensation unit 205 may determine a predictedvideo block for the current video block based on the motion informationand decoded samples of pictures from buffer 213 other than the pictureassociated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may performdifferent operations for a current video block, for example, dependingon whether the current video block is in an I slice, a P slice, or a Bslice.

In some examples, motion estimation unit 204 may perform uni-directionalprediction for the current video block, and motion estimation unit 204may search reference pictures of list 0 or list 1 for a reference videoblock for the current video block. Motion estimation unit 204 may thengenerate a reference index that indicates the reference picture in list0 or list 1 that contains the reference video block and a motion vectorthat indicates a spatial displacement between the current video blockand the reference video block. Motion estimation unit 204 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the current video block. Motioncompensation unit 205 may generate the predicted video block of thecurrent block based on the reference video block indicated by the motioninformation of the current video block.

In other examples, motion estimation unit 204 may perform bi-directionalprediction for the current video block, motion estimation unit 204 maysearch the reference pictures in list 0 for a reference video block forthe current video block and may also search the reference pictures inlist 1 for another reference video block for the current video block.Motion estimation unit 204 may then generate reference indexes thatindicate the reference pictures in list 0 and list 1 containing thereference video blocks and motion vectors that indicate spatialdisplacements between the reference video blocks and the current videoblock. Motion estimation unit 204 may output the reference indexes andthe motion vectors of the current video block as the motion informationof the current video block. Motion compensation unit 205 may generatethe predicted video block of the current video block based on thereference video blocks indicated by the motion information of thecurrent video block.

In some examples, motion estimation unit 204 may output a full set ofmotion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may not output a full setof motion information for the current video. Rather, motion estimationunit 204 may signal the motion information of the current video blockwith reference to the motion information of another video block. Forexample, motion estimation unit 204 may determine that the motioninformation of the current video block is sufficiently similar to themotion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntaxstructure associated with the current video block, a value thatindicates to the video decoder 300 that the current video block has thesame motion information as the other video block.

In another example, motion estimation unit 204 may identify, in a syntaxstructure associated with the current video block, another video blockand a motion vector difference (MVD). The motion vector differenceindicates a difference between the motion vector of the current videoblock and the motion vector of the indicated video block. The videodecoder 300 may use the motion vector of the indicated video block andthe motion vector difference to determine the motion vector of thecurrent video block.

As discussed above, video encoder 200 may predictively signal the motionvector. Two examples of predictive signalling techniques that may beimplemented by video encoder 200 include advanced motion vectorpredication (AMVP) and merge mode signalling.

Intra prediction unit 206 may perform intra prediction on the currentvideo block. When intra prediction unit 206 performs intra prediction onthe current video block, intra prediction unit 206 may generateprediction data for the current video block based on decoded samples ofother video blocks in the same picture. The prediction data for thecurrent video block may include a predicted video block and varioussyntax elements.

Residual generation unit 207 may generate residual data for the currentvideo block by subtracting (e.g., indicated by the minus sign) thepredicted video block(s) of the current video block from the currentvideo block. The residual data of the current video block may includeresidual video blocks that correspond to different sample components ofthe samples in the current video block.

In other examples, there may be no residual data for the current videoblock for the current video block, for example in a skip mode, andresidual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transformcoefficient video blocks for the current video block by applying one ormore transforms to a residual video block associated with the currentvideo block.

After transform processing unit 208 generates a transform coefficientvideo block associated with the current video block, quantization unit209 may quantize the transform coefficient video block associated withthe current video block based on one or more quantization parameter (QP)values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may applyinverse quantization and inverse transforms to the transform coefficientvideo block, respectively, to reconstruct a residual video block fromthe transform coefficient video block. Reconstruction unit 212 may addthe reconstructed residual video block to corresponding samples from oneor more predicted video blocks generated by the predication unit 202 toproduce a reconstructed video block associated with the current blockfor storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loopfiltering operation may be performed to reduce video blocking artifactsin the video block.

Entropy encoding unit 214 may receive data from other functionalcomponents of the video encoder 200. When entropy encoding unit 214receives the data, entropy encoding unit 214 may perform one or moreentropy encoding operations to generate entropy encoded data and outputa bitstream that includes the entropy encoded data.

FIG. 9 is a block diagram illustrating an example of video decoder 300which may be video decoder 114 in the system 100 illustrated in FIG. 7.

The video decoder 300 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 8, the videodecoder 300 includes a plurality of functional components. Thetechniques described in this disclosure may be shared among the variouscomponents of the video decoder 300. In some examples, a processor maybe configured to perform any or all of the techniques described in thisdisclosure.

In the example of FIG. 9, video decoder 300 includes an entropy decodingunit 301, a motion compensation unit 302, an intra prediction unit 303,an inverse quantization unit 304, an inverse transformation unit 305,and a reconstruction unit 306 and a buffer 307. Video decoder 300 may,in some examples, perform a decoding pass generally reciprocal to theencoding pass described with respect to video encoder 200 (FIG. 8).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encodedbitstream may include entropy coded video data (e.g., encoded blocks ofvideo data). Entropy decoding unit 301 may decode the entropy codedvideo data, and from the entropy decoded video data, motion compensationunit 302 may determine motion information including motion vectors,motion vector precision, reference picture list indexes, and othermotion information. Motion compensation unit 302 may, for example,determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used with sub-pixelprecision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used byvideo encoder 200 during encoding of the video block to calculateinterpolated values for sub-integer pixels of a reference block. Motioncompensation unit 302 may determine the interpolation filters used byvideo encoder 200 according to received syntax information and use theinterpolation filters to produce predictive blocks.

Motion compensation unit 302 may use some of the syntax information todetermine sizes of blocks used to encode frame(s) and/or slice(s) of theencoded video sequence, partition information that describes how eachmacroblock of a picture of the encoded video sequence is partitioned,modes indicating how each partition is encoded, one or more referenceframes (and reference frame lists) for each inter-encoded block, andother information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for examplereceived in the bitstream to form a prediction block from spatiallyadjacent blocks. Inverse quantization unit 304 inverse quantizes, i.e.,de-quantizes, the quantized video block coefficients provided in thebitstream and decoded by entropy decoding unit 301. Inverse transformunit 305 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with thecorresponding prediction blocks generated by motion compensation unit302 or intra-prediction unit 303 to form decoded blocks. If desired, adeblocking filter may also be applied to filter the decoded blocks inorder to remove blockiness artifacts. The decoded video blocks are thenstored in buffer 307, which provides reference blocks for subsequentmotion compensation/intra predication and also produces decoded videofor presentation on a display device.

FIGS. 10-26 show example methods that can implement the technicalsolution described above in, for example, the embodiments shown in FIGS.5-9.

FIG. 10 shows a flowchart for an example method 1000 of videoprocessing. The method 1000 includes, at operation 1010, performing aconversion between a video and a bitstream of the video, the bitstreamcomprising one or more access units according to a format rule, and theformat rule specifying that an order in which a first message and asecond message that apply to an operation point (OP) are present withinan access unit (AU) such that the first message precedes the secondmessage in a decoding order.

FIG. 11 shows a flowchart for an example method 1100 of videoprocessing. The method 1100 includes, at operation 1110, performing aconversion between a video and a bitstream of the video, the bitstreamcomprising one or more access units according to a format rule, and theformat rule specifying that an order in which a plurality of messagesthat apply to an operation point (OP) are present within an access unitsuch that a first message of the plurality of messages precedes a secondmessage of the plurality of messages in a decoding order.

FIG. 12 shows a flowchart for an example method 1200 of videoprocessing. The method 1200 includes, at operation 1210, performing aconversion between a video comprising a picture and a bitstream of thevideo, the bitstream conforming to a format rule that specifies that anindication of whether a first flag is signalled at a beginning of apicture header associated with the picture, and the first flag beingindicative of whether the picture is an intra random access point (IRAP)picture or a gradual decoding refresh (GDR) picture.

FIG. 13 shows a flowchart for an example method 1300 of videoprocessing. The method 1300 includes, at operation 1310, performing aconversion between a video comprising one or more pictures and abitstream of the video, the bitstream conforming to a format rule thatdisallows coding of a picture of the one or more pictures to include acoded slice network abstraction layer (NAL) unit having a gradualdecoding refresh type and to associate with a flag indicating that thepicture contains mixed types of NAL units.

FIG. 14 shows a flowchart for an example method 1400 of videoprocessing. The method 1400 includes, at operation 1410, performing aconversion between a video comprising one or more pictures and abitstream of the video, the bitstream conforming to a format rule thatallows coding of a picture of the one or more pictures to include acoded slice network access layer (NAL) unit having a gradual decodingrefresh type and to associate with a flag indicating that the picturedoes not contain mixed types of NAL units.

FIG. 15 shows a flowchart for an example method 1500 of videoprocessing. The method 1500 includes, at operation 1510, performing aconversion between a picture of a video and a bitstream of the video,the bitstream conforming to a format rule that specifies whether a firstsyntax element is signalled in a picture parameter set (PPS) associatedwith the picture, the picture comprising one or more slices with a slicetype, and the first syntax element indicating that the slice type issignalled in the picture header due to the first syntax element beingequal to zero, and otherwise indicates that the slice type is signalledin a slice header.

FIG. 16 shows a flowchart for an example method 1600 of videoprocessing. The method 1600 includes, at operation 1610, performing aconversion between a picture of a video and a bitstream of the videoaccording to a rule, the conversion comprising an in-loop filteringprocess, and the rule specifying that a total number of vertical virtualboundaries and a total number of horizontal virtual boundaries relatedto the in-loop filtering process are signalled at a picture-level or asequence-level.

FIG. 17 shows a flowchart for an example method 1700 of videoprocessing. The method 1700 includes, at operation 1710, performing aconversion between a video comprising one or more pictures and abitstream of the video, the bitstream conforming to a format rule thatconditionally allows coding of a picture in one layer using referencepictures from other layers based on a first syntax element indicatingwhether the reference pictures from the other layers are present in thebitstream, and the first syntax element being conditionally signalled inthe bitstream based on a second syntax element that indicates whether anidentifier of a parameter set associated with the picture is not equalto zero.

FIG. 18 shows a flowchart for an example method 1800 of videoprocessing. The method 1800 includes, at operation 1810, performing aconversion between a picture of a video and a bitstream of the video,the bitstream conforming to a format rule that defines a first syntaxelement for enabling (a) a synchronization process for context variablesbefore decoding a coding tree unit (CTU) in the picture and (b) astorage process for the context variables after decoding the CTU, andthe first syntax element being signalled in a sequence parameter set(SPS) associated with the picture.

FIG. 19 shows a flowchart for an example method 1900 of videoprocessing. The method 1900 includes, at operation 1910, performing aconversion between a picture of a video and a bitstream of the video,the bitstream conforming to a format rule that defines a syntax elementfor indicating whether signalling for entry point offsets for tiles ortile-specific CTU rows are present in a slice header of the picture, andthe syntax element being signalled in a sequence parameter set (SPS)associated with the picture.

FIG. 20 shows a flowchart for an example method 2000 of videoprocessing. The method 2000 includes, at operation 2010, performing aconversion between a video and a bitstream of the video according to arule that specifies that a first syntax element, which indicates anumber of parameters for an output layer set (OLS) hypotheticalreference decoder (HRD) in a video parameter set (VPS) associated withthe video, is less than a first predetermined threshold.

FIG. 21 shows a flowchart for an example method 2100 of videoprocessing. The method 2100 includes, at operation 2110, performing aconversion between a video and a bitstream of the video according to arule that specifies that a syntax element, which indicates a number ofprofile/tier/level (PTL) syntax structures in a video parameter set(VPS) associated with the video, is less than a predetermined threshold.

FIG. 22 shows a flowchart for an example method 2200 of videoprocessing. The method 2200 includes, at operation 2210, performing aconversion between a video and a bitstream of the video according to arule that specifies that a first syntax element, which indicates anumber of decoded picture buffer parameters syntax structures in a videoparameters set (VPS), may be less than or equal to a second syntaxelement, which indicates a number of layers specified by the VPS.

FIG. 23 shows a flowchart for an example method 2300 of videoprocessing. The method 2300 includes, at operation 2310, performing aconversion between a video and a bitstream of the video according to arule that allows a terminating network abstraction layer (NAL) unit tobe made available to a decoder by signalling in the bitstream orproviding through external means.

FIG. 24 shows a flowchart for an example method 2400 of videoprocessing. The method 2400 includes, at operation 2410, performing aconversion between a video and a bitstream of the video, the bitstreamconforming to a format rule that restricts each layer in the bitstreamto contain only one subpicture due to a syntax element being equal tozero, which indicates that the each layer is configured to useinter-layer prediction.

FIG. 25 shows a flowchart for an example method 2500 of videoprocessing. The method 2500 includes, at operation 2510, performing aconversion between a video and a bitstream of the video according to arule that specifies that a sub-bitstream extraction process isimplemented to generate a sub-bitstream for decoding, wherein thesub-bitstream extraction process is configured to extract, from thebitstream, a sub-bitstream with a target highest temporal identifier,and the rule further specifying that, during the extracting, uponremoving a video coding layer (VCL) network abstraction layer (NAL)unit, filler data units and filler supplemental enhancement information(SEI) messages in SEI NAL units that are associated with the VCL NALunit are also removed.

FIG. 26 shows a flowchart for an example method 2600 of videoprocessing. The method 2600 includes, at operation 2610, performing aconversion between a video unit of a video and a bitstream of the video,the bitstream conforming to a format rule that specifies that thebitstream includes a first syntax element, which indicates whether thevideo unit is coded in a lossless mode or in a lossy mode, andsignalling a second syntax element, which indicates an escape sample ina palette mode applied to the video unit, being selectively includedbased on a value of the first syntax element.

A listing of solutions preferred by some embodiments is provided next.

A1. A method of video processing, comprising performing a conversionbetween a video and a bitstream of the video, wherein the bitstreamcomprises one or more access units according to a format rule, andwherein the format rule specifies an order in which a first message anda second message that apply to an operation point (OP) are presentwithin an access unit (AU) such that the first message precedes thesecond message in a decoding order.

A2. The method of solution A1, wherein the first message comprises abuffering period (BP) supplemental enhancement information (SEI) messageand the second message comprises a picture timing (PT) SEI message.

A3. The method of solution A1, wherein the first message comprises abuffering period (BP) supplemental enhancement information (SEI) messageand the second message comprises a decoding unit information (DUI) SEImessage.

A4. The method of solution A1, wherein the first message comprises apicture timing (PT) supplemental enhancement information (SEI) messageand the second message comprises a decoding unit information (DUI) SEImessage.

A5. A method of video processing, comprising performing a conversionbetween a video and a bitstream of the video, wherein the bitstreamcomprises one or more access units according to a format rule, andwherein the format rule specifies an order in which a plurality ofmessages that apply to an operation point (OP) are present within anaccess unit such that a first message of the plurality of messagesprecedes a second message of the plurality of messages in a decodingorder.

A6. The method of solution A5, wherein the plurality of messagescomprises a buffering period (BP) SEI message, a decoding unitinformation (DUI) SEI message, a picture timing (PT) SEI message, and asubpicture level information (SLI) SEI message.

A7. The method of solution A6, wherein the decoding order is the SLI SEImessage, the BP SEI message, the PT SEI message, and the DUI message.

Another listing of solutions preferred by some embodiments is providednext.

B1. A method of video processing, comprising performing a conversionbetween a video comprising a picture and a bitstream of the video,wherein the bitstream conforms to a format rule, wherein the format rulespecifies that an indication of whether a first flag is signalled at abeginning of a picture header associated with the picture, wherein thefirst flag is indicative of whether the picture is an intra randomaccess point (IRAP) picture or a gradual decoding refresh (GDR) picture.

B2. The method of solution B 1, wherein the IRAP picture is a picturethat, when a decoding of the bitstream starts at the picture, thepicture and all subsequent pictures in an output order can be correctlydecoded.

B3. The method of solution B1, wherein the IRAP picture contains only Islices.

B4. The method of solution B1, wherein the GDR picture is a picturethat, when the decoding of the bitstream starts at the picture, acorresponding recovery point picture and all subsequent pictures in botha decoding order and the output order can be correctly decoded.

B5. The method of solution B1, wherein the format rule further specifiesthat whether a second flag is signalled in the bitstream is based on theindication.

B6. The method of solution B5, wherein the first flag isirap_or_gdr_pic_flag.

B7. The method of solution B6, wherein the second flag isno_output_of_prior_pics_flag.

B8. The method of any of solutions B1 to B7, wherein the first flagbeing equal to one indicates that the picture is an IRAP picture or aGDR picture.

B9. The method of any of solutions B1 to B7, wherein the first flagbeing equal to zero indicates that the picture is neither an IRAPpicture nor a GDR picture.

B10. The method of any of solutions B1 to B9, wherein each networkaccess layer (NAL) unit in the GDR picture has a nal_unit_type syntaxelement equal to GDR_NUT.

Yet another listing of solutions preferred by some embodiments isprovided next.

C1. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures and a bitstream of thevideo, wherein the bitstream conforms to a format rule, wherein theformat rule disallows coding of a picture of the one or more pictures toinclude a coded slice network abstraction layer (NAL) unit having agradual decoding refresh type and to associate with a flag indicatingthat the picture contains mixed types of NAL units.

C2. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures and a bitstream of thevideo, wherein the bitstream conforms to a format rule, wherein theformat rule allows coding of a picture of the one or more pictures toinclude a coded slice network access layer (NAL) unit having a gradualdecoding refresh type and to associate with a flag indicating that thepicture does not contain mixed types of NAL units.

C3. The method of solution C1 or C2, wherein the flag ismixed_nalu_types_in_pic_flag.

C4. The method of solution C3, wherein the flag is in a pictureparameter set (PPS).

C5. The method of any of solutions C1 to C4, wherein the picture is agradual decoding refresh (GDR) picture, and wherein each slice or NALunit in the picture has a nal_unit_type equal to GDR_NUT.

C6. A method of video processing, comprising performing a conversionbetween a picture of a video and a bitstream of the video, wherein thebitstream conforms to a format rule that specifies whether a firstsyntax element is signalled in a picture parameter set (PPS) associatedwith the picture, wherein the picture comprises one or more slices witha slice type, wherein the first syntax element indicates that the slicetype is signalled in the picture header due to the first syntax elementbeing equal to zero, and otherwise indicates that the slice type issignalled in a slice header.

C7. The method of solution C6, wherein the first syntax element ismixed_slice_types_in_pic_flag.

C8. The method of solution C6 or C7, wherein the first syntax element issignalled due to a second syntax element being equal to zero and/or athird syntax element being greater than zero.

C9. The method of solution C8, wherein the second syntax elementspecifies at least one characteristic of one or more tiles within eachof the one or more slices.

C10. The method of solution C9, wherein the second syntax elementequaling zero specifies that the one or more tiles are in raster scanorder and slice information is excluded from the PPS.

C11. The method of solution C9, wherein the second syntax elementequaling one specifies that the one or more tiles cover a rectangularregion of the picture and slice information is signalled in the PPS.

C12. The method of any of solutions C9 to C11, wherein the second syntaxelement is rect_slice_flag.

C13. The method of solution C8, wherein the third syntax elementspecifies a number of rectangular slices in the picture that refer tothe PPS.

C14. The method of solution C13, wherein the third syntax element isnum_slices_in_pic_minus1.

C15. A method of video processing, comprising performing a conversionbetween a picture of a video and a bitstream of the video according to arule, wherein the conversion comprises an in-loop filtering process, andwherein the rule specifies that a total number of vertical virtualboundaries and a total number of horizontal virtual boundaries relatedto the in-loop filtering process are signalled at a picture-level or asequence-level.

C16. The method of solution C15, wherein the total number of verticalvirtual boundaries comprise up to a first number (N1) of verticalvirtual boundaries that are signalled in a picture parameter set (PPS)or a sequence parameter set (SPS) and up to a second number (N3) ofextra vertical virtual boundaries that are signalled in a picture header(PH), and wherein the total number of horizontal virtual boundariescomprise up to a third number (N2) of horizontal virtual boundaries thatare signalled in the PPS or the SPS and up to a fourth number (N4) ofextra horizontal virtual boundaries that are signalled in the PH.

C17. The method of solution C16, wherein N1+N3≤N1 and N2+N4≤N2.

C18. The method of solution C16 or C17, wherein N1=3, N2=3, N3=1, andN4=1.

Yet another listing of solutions preferred by some embodiments isprovided next.

D1. A method of video processing, comprising performing a conversionbetween a video comprising one or more pictures and a bitstream of thevideo, wherein the bitstream conforms to a format rule, wherein theformat rule conditionally allows coding of a picture in one layer usingreference pictures from other layers based on a first syntax elementindicating whether the reference pictures from the other layers arepresent in the bitstream, and wherein the first syntax element isconditionally signalled in the bitstream based on a second syntaxelement that indicates whether an identifier of a parameter setassociated with the picture is not equal to zero.

D2. The method of solution D1, wherein the first syntax element isinter_layer_ref_pics_present_flag.

D3. The method of solution D1 or D2, wherein the first syntax elementspecifies whether an inter-layer prediction is enabled and aninter-layer reference picture can be used.

D4. The method of solution D1, wherein the first syntax element issps_inter_layer_prediction_enabled_flag.

D5. The method of any of solutions D1 to D4, wherein the first syntaxelement is in a sequence parameter set (SPS).

D6. The method of any of solutions D1 to D4, wherein the parameter setis a video parameter set (VPS).

D7. The method of solution D6, wherein the second syntax element issps_video_parameter_set_id.

D8. The method of solution D6 or D7, wherein the parameter set providesan identifier for the VPS for reference by other syntax elements.

D9. The method of solution D7, wherein the second syntax element is in asequence parameter set (SPS).

Yet another listing of solutions preferred by some embodiments isprovided next.

E1. A method of video processing, comprising performing a conversionbetween a picture of a video and a bitstream of the video, wherein thebitstream conforms to a format rule, wherein the format rule defines afirst syntax element for enabling (a) a synchronization process forcontext variables before decoding a coding tree unit (CTU) in thepicture and (b) a storage process for the context variables afterdecoding the CTU, wherein the first syntax element is signalled in asequence parameter set (SPS) associated with the picture.

E2. The method of solution E1, wherein the first syntax element isexcluded from a picture parameter set (PPS) associated with the picture.

E3. The method of solution E1 or E2, wherein the CTU comprises a firstcoding tree block (CTB) of a row of CTBs in each tile in the picture.

E4. The method of any of solutions E1 to E3, wherein the first syntaxelement is entropy_coding_sync_enabled_flag.

E5. The method of any of solutions E1 to E3, wherein the first syntaxelement is sps_entropy_coding_sync_enabled_flag.

E6. The method of any of solutions E1 to E5, wherein the format ruledefines a second syntax element for indicating whether signalling forentry point offsets for tiles or tile-specific CTU rows are present in aslice header of the picture, and wherein the second syntax element issignalled in the SPS associated with the picture.

E7. A method of video processing, comprising performing a conversionbetween a picture of a video and a bitstream of the video, wherein thebitstream conforms to a format rule, wherein the format rule defines asyntax element for indicating whether signalling for entry point offsetsfor tiles or tile-specific coding tree unit (CTU) rows are present in aslice header of the picture, and wherein the syntax element is signalledin a sequence parameter set (SPS) associated with the picture.

E8. The method of solution E7, wherein the format rule allows signallingof the entry point offsets based on a value of the syntax element beingequal to one.

E9. The method of solution E7 or E8, wherein the syntax element isexcluded from a picture parameter set (PPS) associated with the picture.

E10. The method of any of solutions E7 to E9, wherein the syntax elementis entry_point_offsets_present_flag.

E11. The method of any of solutions E7 to E9, wherein the syntax elementis sps_entry_point_offsets_present_flag.

Yet another listing of solutions preferred by some embodiments isprovided next.

F1. A method of video processing, comprising performing a conversionbetween a video and a bitstream of the video according to a rule,wherein the rule specifies that a first syntax element, which indicatesa number of parameters for an output layer set (OLS) hypotheticalreference decoder (HRD) in a video parameter set (VPS) associated withthe video, is less than a first predetermined threshold.

F2. The method of solution F 1, wherein the first syntax element isvps_num_ols_timing_hrd_params_minus1.

F3. The method of solution F1 or F2, wherein the first predeterminedthreshold is a number of multi-layer output layer sets (denotedNumMultiLayerOlss) minus one.

F4. The method of any of solutions F1 to F3, wherein the first syntaxelement is inferred to be zero when the first syntax element is notsignalled in the bitstream.

F5. The method of any of solutions F1 to F4, wherein the rule specifiesthat a second syntax element, which indicates a number ofprofile/tier/level (PTL) syntax structures in a video parameter set(VPS) associated with the video, is less than a second predeterminedthreshold.

F6. A method of video processing, comprising performing a conversionbetween a video and a bitstream of the video according to a rule,wherein the rule specifies that a syntax element, which indicates anumber of profile/tier/level (PTL) syntax structures in a videoparameter set (VPS) associated with the video, is less than apredetermined threshold.

F7. The method of solution F6, wherein the syntax element isvps_num_ptls_minus1.

F8. The method of solution F6 or F7, wherein the predetermined thresholdis a total number of output layer sets (denoted TotalNumOlss).

F9. The method of any of solutions F1 to F8, wherein a differencebetween the predetermined threshold and the syntax element is signalledin the bitstream.

F10. The method of solution F9, wherein the difference is signalledusing a unary code.

F11. The method of solution F9, wherein the difference is signalledusing an exponential-Golomb (EG) code.

F12. A method of video processing, comprising performing a conversionbetween a video and a bitstream of the video according to a rule,wherein the rule specifies that a first syntax element, which indicatesa number of decoded picture buffer parameters syntax structures in avideo parameters set (VPS), may be less than or equal to a second syntaxelement, which indicates a number of layers specified by the VPS.

F13. The method of solution F12, wherein a difference between the firstsyntax element and a predetermined threshold is signalled in thebitstream.

F14. The method of solution F12, wherein a difference between the secondsyntax element and a predetermined threshold is signalled in thebitstream.

F15. The method of solution F13 or F14, wherein the difference issignalled using a unary code.

F16. The method of solution F13 or F14, wherein the difference issignalled using an exponential-Golomb (EG) code.

F17. A method of video processing, comprising performing a conversionbetween a video and a bitstream of the video according to a rule,wherein the rule allows a terminating network abstraction layer (NAL)unit to be made available to a decoder by signalling in the bitstream orproviding through external means.

F18. The method of solution F17, wherein the terminating NAL unit is anend of bitstream (EOB) NAL unit.

F19. The method of solution F17, wherein the terminating NAL unit is anend of sequence (EOS) NAL unit.

F20. The method of any of solutions F17 to F19, wherein the externalmeans include a parameter set.

F21. A method of video processing, comprising performing a conversionbetween a video and a bitstream of the video, wherein the bitstreamconforms to a format rule, and wherein the format rule restricts eachlayer in the bitstream to contain only one subpicture due to a syntaxelement being equal to zero, which indicates that the each layer isconfigured to use inter-layer prediction.

F22. The method of solution F21, wherein the syntax element isvps_independent_layer_flag.

Yet another listing of solutions preferred by some embodiments isprovided next.

G1. A method of video processing, comprising performing a conversionbetween a video and a bitstream of the video according to a rule,wherein the rule specifies that a sub-bitstream extraction process isimplemented to generate a sub-bitstream for decoding, wherein thesub-bitstream extraction process is configured to extract, from thebitstream, a sub-bitstream with a target highest temporal identifier,and wherein, the rule specifies that, during the extracting, uponremoving a video coding layer (VCL) network abstraction layer (NAL)unit, filler data units and filler supplemental enhancement information(SEI) messages in SEI NAL units that are associated with the VCL NALunit are also removed.

G2. The method of solution G1, wherein the VCL NAL unit is removed basedon an identifier of a layer that the VCL NAL unit belongs to.

G3. The method of solution G2, wherein the identifier is nuh_layer_id.

G4. The method of solution G1, wherein the bitstream conforms to aformat rule that specifies that a SEI NAL unit that comprises a SEImessage with a filler payload does not include SEI messages with apayload different from the filler payload.

G5. The method of solution G1, wherein the bitstream conforms to aformat rule that specifies that a SEI NAL unit that comprises a SEImessage with a filler payload is configured to exclude another SEImessage with any other payload.

G6. The method of solution G1, wherein the VCL NAL unit has a maximum ofone associated filler NAL unit.

G7. A method of video processing, comprising performing a conversionbetween a video unit of a video and a bitstream of the video, whereinthe bitstream conforms to a format rule, wherein the format rulespecifies that the bitstream includes a first syntax element, whichindicates whether the video unit is coded in a lossless mode or in alossy mode, and wherein signalling a second syntax element, whichindicates an escape sample in a palette mode applied to the video unit,is selectively included based on a value of the first syntax element.

G8. The method of solution G7, wherein a binarization method of theescape sample is based on the first syntax element.

G9. The method of solution G7, wherein a determination of a contextcoding in an arithmetic coding for the escape sample is based on theflag.

G10. The method of any of solutions G7 to G9, wherein the video unit isa coding unit (CU) or a coding tree unit (CTU).

Yet another listing of solutions preferred by some embodiments isprovided next.

P1. A method of video processing, comprising performing a conversionbetween a picture of a video and a coded representation of the video,wherein a number of subpictures in the picture is included in the codedrepresentation as a field whose bit width is dependent on a value of thenumber of subpictures.

P2. The method of solution P1, wherein the field represents the numberof subpictures using a codeword.

P3. The method of solution P2, wherein the codeword comprises a Golombcodeword.

P4. The method of any of solutions P1 to P3, wherein the value of thenumber of subpictures is restricted to be less than or equal to aninteger number of coding tree blocks that fit within the picture.

P5. The method of any of solutions P1 to P4, wherein the field isdependent on a coding level associated with the coded representation.

P6. A method of video processing, comprising performing a conversionbetween a video region of a video and a coded representation of thevideo, wherein the coded representation conforms to a format rule,wherein the format rule specifies to omit a syntax element indicative ofsubpicture identifiers due to the video region not comprising anysubpictures.

P7. The method of solution P6, wherein the coded representation includesa field having a 0 value indicating that the video region is notcomprising any subpictures.

P8. A method of video processing, comprising performing a conversionbetween a video region of a video and a coded representation of thevideo, wherein the coded representation conforms to a format rule,wherein the format rule specifies to omit identifiers of subpictures inthe video region at a video region header level in the codedrepresentation.

P9. The method of solution P8, wherein the coded representationidentifies subpictures numerically according to an order in which thesubpictures are listed in the video region header.

P10. A method of video processing, comprising performing a conversionbetween a video region of a video and a coded representation of thevideo, wherein the coded representation conforms to a format rule,wherein the format rule specifies to include identifiers of subpicturesand/or a length of the identifiers of subpictures in the video region ata sequence parameter set level or a picture parameter set level.

P11. The method of solution P10, wherein the length is included in thepicture parameter set level.

P12. A method of video processing, comprising performing a conversionbetween a video region of a video and a coded representation of thevideo, wherein the coded representation conforms to a format rule,wherein the format rule specifies to include a field in the codedrepresentation at a video sequence level to indicate whether asubpicture identifier length field is included in the codedrepresentation at the video sequence level.

P13. The method of solution P12, wherein the format rule specifies toset the field to “1” in case that another field in the codedrepresentation indicates that a length identifier for the video regionis included in the coded representation.

P14. A method of video processing, comprising performing a conversionbetween a video region of a video and a coded representation of thevideo, wherein the coded representation conforms to a format rule, andwherein the format rule specifies to include an indication in the codedrepresentation to indicate whether the video region can be used as areference picture.

P15. The method of solution P14, wherein the indication comprises alayer ID and an index or an ID value associated with the video region.

P16. A method of video processing, comprising performing a conversionbetween a video region of a video and a coded representation of thevideo, wherein the coded representation conforms to a format rule, andwherein the format rule specifies to include an indication in the codedrepresentation to indicate whether the video region may use inter-layerprediction (ILP) from a plurality of sample values associated with videoregions of reference layers.

P17. The method of solution P16, wherein the indication is included at asequence level, a picture level or a video level.

P18. The method of solution P16, wherein the video regions of thereference layers comprise at least one collocated sample of a samplewithin the video region.

P19. The method of solution P16, wherein the indication is included inone or more supplemental enhancement information (SEI) messages.

P20. A method of video processing, comprising configuring, upon adetermination that a first message and a second message that apply to anoperation point in an access unit of a video are present in a codedrepresentation of the video, the coded representation such the firstmessage precedes the second message in decoding order; and performing,based on the configuring, a conversion between a video region of thevideo and the coded representation.

Dd the

P22. The method of solution P20, wherein the first message comprises abuffering period (BP) supplemental enhancement information (SEI) messageand the second message comprises a decoding unit information (DUI) SEImessage.

P23. The method of solution P20, wherein the first message comprises apicture timing (PT) supplemental enhancement information (SEI) messageand the second message comprises a decoding unit information (DUI) SEImessage.

P24. The method of any of the above claims, wherein the video regioncomprises a subpicture of the video.

P25. The method of any of the above claims, wherein the conversioncomprises parsing and decoding the coded representation to generate thevideo.

P26. The method of any of the above claims, wherein the conversioncomprises encoding the video to generate the coded representation.

P27. A video decoding apparatus comprising a processor configured toimplement a method recited in one or more of solutions P1 to P26.

P28. A video encoding apparatus comprising a processor configured toimplement a method recited in one or more of solutions P1 to P26.

P29. A computer program product having computer code stored thereon, thecode, when executed by a processor, causes the processor to implement amethod recited in any of solutions P1 to P26.

The following solutions apply to the technical solutions listed above.

O1. The method of any of the preceding solutions, wherein the conversioncomprises decoding the video from the bitstream representation.

O2. The method of any of the preceding solutions, wherein the conversioncomprises encoding the video into the bitstream representation.

O3. The method of any of the preceding solutions, wherein the conversioncomprises generating the bitstream from the video, and wherein themethod further comprises storing the bitstream in a non-transitorycomputer-readable recording medium.

O4. A method of storing a bitstream representing a video to acomputer-readable recording medium, comprising generating a bitstreamfrom a video according to a method described in any of the precedingsolutions; and writing the bitstream to the computer-readable recordingmedium.

O5. A video processing apparatus comprising a processor configured toimplement a method recited in any of the preceding solutions.

O6. A computer-readable medium having instructions stored thereon, theinstructions, when executed, causing a processor to implement a methodrecited in any of the preceding solutions.

O7. A computer readable medium that stores the bitstream representationgenerated according to any of the preceding solutions.

O8. A video processing apparatus for storing a bitstream representation,wherein the video processing apparatus is configured to implement amethod recited in any of the preceding solutions.

O9. A bitstream that is generated using a method recited in any of thepreceding solutions, the bitstream being stored on a computer-readablemedium.

The disclosed and other solutions, examples, embodiments, modules andthe functional operations described in this document can be implementedin digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this document and theirstructural equivalents, or in combinations of one or more of them. Thedisclosed and other embodiments can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a computer readable medium for execution by, orto control the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an field programmable gate array (FPGA) or anapplication specific integrated circuit (ASIC).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computermay not need to have such devices. Computer readable media suitable forstoring computer program instructions and data include all forms ofnon-volatile memory, media and memory devices, including by way ofexample semiconductor memory devices, e.g., erasable programmableread-only memory (EPROM), electrically EPROM (EEPROM), and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto optical disks; and compact disc read-only memory (CD ROM) anddigital versatile disc read-only memory (DVD-ROM) disks. The processorand the memory can be supplemented by, or incorporated in, specialpurpose logic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any subject matter or of whatmay be claimed, but rather as descriptions of features that may bespecific to particular embodiments of particular techniques. Certainfeatures that are described in this patent document in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a sub combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method of video processing, comprising:performing a conversion between a video comprising one or more picturesand a bitstream of the video, wherein the bitstream conforms to a formatrule, wherein the format rule conditionally allows coding of the one ormore pictures in one layer using a reference picture from other layersbased on a first syntax element indicating whether an inter-layerprediction is enabled and whether an inter-layer reference picture iscapable of being used, and wherein the first syntax element isconditionally present in the bitstream based on a second syntax elementthat indicates whether an identifier of a video parameter set (VPS)associated with the one or more pictures is not equal to zero.
 2. Themethod of claim 1, wherein the first syntax element is in a sequenceparameter set (SPS), and wherein the first syntax element issps_inter_layer_prediction_enabled_flag.
 3. The method of claim 1,wherein the second syntax element is in a sequence parameter set (SPS),and wherein the second syntax element is sps_video_parameter_set_id. 4.The method of claim 1, wherein the format rule defines a third syntaxelement for enabling (a) a synchronization process for context variablesbefore decoding a coding tree unit (CTU) in each picture of the one ormore pictures and (b) a storage process for the context variables afterdecoding the CTU, wherein the third syntax element is present in asequence parameter set (SPS) associated with the one or more pictures,and wherein the third syntax element is excluded from a pictureparameter set (PPS) associated with the one or more pictures.
 5. Themethod of claim 4, wherein the CTU comprises a first coding tree block(CTB) of a row of CTBs in each tile in each picture of the one or morepictures.
 6. The method of claim 4, wherein the third syntax element issps_entropy_coding_sync_enabled_flag.
 7. The method of claim 1, whereinthe format rule further defines a fourth syntax element indicatingwhether signaling entry point offsets for tiles or tile-specific codingtree unit (CTU) rows are allowed to be present in a slice header of apicture of the one or more pictures, wherein the fourth syntax elementis present in a sequence parameter set (SPS) associated with the one ormore pictures, and wherein the fourth syntax element is excluded from apicture parameter set (PPS) associated with the one or more pictures. 8.The method of claim 7, wherein the format rule allows signalling of theentry point offsets based on a value of the fourth syntax element beingequal to one.
 9. The method of claim 7, wherein the fourth syntaxelement is sps_entry_point_offsets_present_flag.
 10. The method of claim1, wherein the conversion comprises decoding the video from thebitstream.
 11. The method of claim 1, wherein the conversion comprisesencoding the video into the bitstream.
 12. An apparatus for processingvideo data comprising a processor and a non-transitory memory withinstructions thereon, wherein the instructions upon execution by theprocessor, cause the processor to: perform a conversion between a videocomprising one or more pictures and a bitstream of the video, whereinthe bitstream conforms to a format rule, wherein the format ruleconditionally allows coding of the one or more pictures in one layerusing a reference picture from other layers based on a first syntaxelement indicating whether an inter-layer prediction is enabled andwhether an inter-layer reference picture is capable of being used, andwherein the first syntax element is conditionally present in thebitstream based on a second syntax element that indicates whether anidentifier of a video parameter set (VPS) associated with the one ormore pictures is not equal to zero.
 13. The apparatus of claim 12,wherein the first syntax element and the second syntax element arepresent in a sequence parameter set (SPS) associated with the one ormore pictures, wherein the first syntax element issps_inter_layer_prediction_enabled_flag, and wherein the second syntaxelement is sps_video_parameter_set_id.
 14. The apparatus of claim 12,wherein the format rule defines a third syntax element for enabling (a)a synchronization process for context variables before decoding a codingtree unit (CTU) in each picture of the one or more pictures and (b) astorage process for the context variables after decoding the CTU,wherein the format rule further defines a fourth syntax elementindicating whether signalling entry point offsets for tiles ortile-specific coding tree unit (CTU) rows are allowed to be present in aslice header of a picture of the one or more pictures, wherein the thirdsyntax element and the fourth syntax element are present in a sequenceparameter set (SPS) associated with the one or more pictures, andwherein the third syntax element and the fourth syntax element areexcluded from a picture parameter set (PPS) associated with the one ormore pictures.
 15. A non-transitory computer-readable storage mediumstoring instructions that cause a processor to: perform a conversionbetween a video comprising one or more pictures and a bitstream of thevideo, wherein the bitstream conforms to a format rule, wherein theformat rule conditionally allows coding of the one or more pictures inone layer using a reference picture from other layers based on a firstsyntax element indicating whether an inter-layer prediction is enabledand whether an inter-layer reference picture is capable of being used,and wherein the first syntax element is conditionally present in thebitstream based on a second syntax element that indicates whether anidentifier of a video parameter set (VPS) associated with the one ormore pictures is not equal to zero.
 16. The non-transitorycomputer-readable storage medium of claim 15, wherein the first syntaxelement and the second syntax element are present in a sequenceparameter set (SPS) associated with the one or more pictures, whereinthe first syntax element is sps_inter_layer_prediction_enabled_flag, andwherein the second syntax element is sps_video_parameter_set_id.
 17. Thenon-transitory computer-readable storage medium of claim 15, wherein theformat rule defines a third syntax element for enabling (a) asynchronization process for context variables before decoding a codingtree unit (CTU) in each picture of the one or more pictures and (b) astorage process for the context variables after decoding the CTU,wherein the format rule further defines a fourth syntax elementindicating whether signaling entry point offsets for tiles ortile-specific CTU rows are allowed to be present in a slice header of apicture of the one or more pictures, wherein the third syntax elementand the fourth syntax element are present in a sequence parameter set(SPS) associated with the one or more pictures, and wherein the thirdsyntax element and the fourth syntax element are excluded from a pictureparameter set (PPS) associated with the one or more pictures.
 18. Anon-transitory computer-readable recording medium storing a bitstream ofa video which is generated by a method performed by a video processingapparatus, wherein the method comprises: generating the bitstream of thevideo comprising one or more pictures, wherein the bitstream conforms toa format rule, wherein the format rule conditionally allows coding ofthe one or more pictures in one layer using a reference picture fromother layers based on a first syntax element indicating whether aninter-layer prediction is enabled and whether an inter-layer referencepicture is capable of being used, and wherein the first syntax elementis conditionally present in the bitstream based on a second syntaxelement that indicates whether an identifier of a video parameter set(VPS) associated with the one or more pictures is not equal to zero. 19.The non-transitory computer-readable recording medium of claim 18,wherein the first syntax element and the second syntax element arepresent in a sequence parameter set (SPS) associated with the one ormore pictures, wherein the first syntax element issps_inter_layer_prediction_enabled_flag, and wherein the second syntaxelement is sps_video_parameter_set_id.
 20. The non-transitorycomputer-readable recording medium of claim 18, wherein the format ruledefines a third syntax element for enabling (a) a synchronizationprocess for context variables before decoding a coding tree unit (CTU)in each picture of the one or more pictures and (b) a storage processfor the context variables after decoding the CTU, wherein the formatrule further defines a fourth syntax element indicating whethersignalling entry point offsets for tiles or tile-specific CTU rows areallowed to be present in a slice header of a picture of the one or morepictures, wherein the third syntax element and the fourth syntax elementare present in a sequence parameter set (SPS) associated with the one ormore pictures, and wherein the third syntax element and the fourthsyntax element are excluded from a picture parameter set (PPS)associated with the one or more pictures.